基本情報

所属

• 電子科学研究所　物質科学研究部門

職名

• 教授

ホームページURL

http://www.aist.go.jp/RESEARCHERDB/cgi-bin/worker_detail.cgi?call=namae&rw_id=V90451526

J-Global ID

• 200901096020953212

研究分野

• ナノテク・材料 / ナノ材料科学

担当教育組織

•  修士課程　環境科学院
•  博士課程　環境科学院

研究活動情報

論文

• Self-assembled halide perovskite quantum dots in polymer thin films showing temperature-controlled exciton recombination.

  Most Farida Khatun, Takuya Okamoto, Vasudevanpillai Biju

  Chemical communications (Cambridge, England) 2023年10月20日 

  Rationally assembled supramolecular structures of organic chromophores or semiconductor nanomaterials show excitonic properties different from individual molecules or nanoparticles. We report polymer-assisted assembly formation and thermal modulation of excitonic recombination in self-assembled formamidinium lead bromide perovskite quantum dots.
• Highly Luminescent and Stable Halide Perovskite Nanocrystals by Interfacial Defect Passivation and Amphiphilic Ligand Capping.

  Sushant Ghimire, Most Farida Khatun, Bhagyashree M Sachith, Takuya Okamoto, Jeladhara Sobhanan, Ch Subrahmanyam, Vasudevanpillai Biju

  ACS applied materials & interfaces 15 34 41081 - 41091 2023年08月30日 [査読有り]
   

  Halide vacancies cause lattice degradation and nonradiative losses in halide perovskites. In this study, we strategically fill bromide vacancies in CsPbBr3 perovskite nanocrystals with NaBr, KBr, or CsBr at the organic-aqueous interface for hydrophobic ligand-capped nanocrystals or in a polar solvent (2-propanol) for amphiphilic ligand-capped nanocrystals. Energy-dispersive X-ray spectra, powder X-ray diffraction data, and scanning transmission electron microscopy images help us confirm vacancy filling and the structures of samples. The bromide salts increase the photoluminescence quantum yield (98 ± 2%) of CsPbBr3 by decreasing the nonradiative decay rate. Single-particle studies show the quantum yield increase originates from the poorly luminescent nanocrystals becoming highly luminescent after filling vacancies. Furthermore, we tune the optical band gap (ultraviolet-visible-near-infrared) of the hydrophobic ligand-capped nanocrystals by halide exchange at the toluene-water interface using saturated NaCl or NaI solutions, which completes in about 60 min under continuous mixing. In contrast, the amphiphilic ligand accelerates the halide exchange in 2-propanol, suggesting ambipolar functional groups speed up the ion-exchange reaction. The bromide vacancy-filled or halide-exchanged samples in a toluene-water biphasic solvent show higher stability than amphiphilic ligand-capped samples in 2-propanol. This strategy of defect passivation, ion exchange, and ligand chemistry to improve quantum yields and tune band gaps of halide perovskite nanocrystals can be promising for designing stable and water-soluble perovskite samples for solar cells, light-emitting diodes, photodetectors, and photocatalysts.
• Thermodynamically and Kinetically Controlled Nucleation and Growth of Halide Perovskite Single Crystals.

  Dong Zhang, Takuya Okamoto, Vasudevanpillai Biju

  Small (Weinheim an der Bergstrasse, Germany) e2304900  2023年07月25日 [査読有り]
   

  Halide perovskites are ideal for next-generation optical devices and photovoltaics. Although perovskite single-crystals show reproducible optoelectronic properties, significant variations in the crystal size, anisotropy, density, defects, photoluminescence (PL), and carrier lifetime affect the sample properties and device performances. Homogenous size and shape FA/MAPbBr3 single microcrystals (MCs) with controlled edge lengths, crystal densities, PL lifetimes, and PL intensities are prepared by thermodynamically controlling and kinetically separating the crystal nucleation-growth processes using optimum N-cyclohexyl-2-pyrrolidone (CHP) concentration. The crystal growth kinetics at different CHP concentrations and temperatures are estimated spectroscopically by measuring the concentration of Pb (II). High-density cubic MCs with a homogenous size distribution, high PL intensities, and long PL lifetimes are obtained within minutes at high temperatures by the controlled addition of the pyrrolidone derivative. Conversely, the crystal size nonlinearly increases with time at low temperatures. The isotropically grown high-density single crystals at controlled nucleation-growth rates at 190 °C with 20% CHP show the highest PL intensity and the longest PL lifetimes. This method offers thermodynamic and kinetic control of perovskite single-crystal growth with shape control.
• Slipping-Free Halide Perovskite Supercrystals from Supramolecularly-Assembled Nanocrystals.

  Takuya Okamoto, Vasudevanpillai Biju

  Small (Weinheim an der Bergstrasse, Germany) e2303496  2023年05月12日 [査読有り]
   

  Supramolecularly assembled high-order supercrystals (SCs) help control the dielectric, electronic, and excitonic properties of semiconductor nanocrystals (NCs) and quantum dots (QDs). Ligand-engineered perovskite NCs (PNCs) assemble into SCs showing shorter excitonic lifetimes than strongly dielectric PNC films showing long photoluminescence (PL) lifetimes and long-range carrier diffusion. Monodentate to bidentate ligand exchange on ≈ 8 nm halide perovskite (APbX3 ; A:Cs/MA, X:Br/I) PNCs generates mechanically stable SCs with close-packed lattices, overlapping electronic wave functions, and higher dielectric constant, providing distinct excitonic properties from single PNCs or PNC films. From Fast Fourier Transform (FFT) images, time-resolved PL, and small-angle X-ray scattering, structurally and excitonically ordered large SCs are identified. An Sc shows a smaller spectral shift (<35 meV) than a PNC film (>100 meV), a microcrystal (>100 meV), or a bulk crystal (>100 meV). Also, the exciton lifetime (<10 ns) of an SC is excitation power-independent in the single exciton regime 〈N〉<1, comparable to an isolated PNC. Therefore, bidentate-ligand-assisted SCs help overcome delayed exciton or carrier recombination in halide perovskite nanocrystal assemblies or films.
• Photoinduced interfacial electron transfer from perovskite quantum dots to molecular acceptors for solar cells.

  Bhagyashree Mahesha Sachith, Zhijing Zhang, Palyam Subramanyam, Challapalli Subrahmanyam, Akihiro Furube, Naoto Tamai, Takuya Okamoto, Hiroaki Misawa, Vasudevanpillai Biju

  Nanoscale 15 17 7695 - 7702 2023年05月04日 [査読有り]
   

  Bandgap-engineered inorganic and hybrid halide perovskite (HP) films, nanocrystals, and quantum dots (PQDs) are promising for solar cells. Fluctuations of photoinduced electron transfer (PET) rates affect the interfacial charge separation efficiencies of such solar cells. Electron donor- or acceptor-doped perovskite samples help analyze PET and harvest photogenerated charge carriers efficiently. Therefore, PET in perovskite-based donor-acceptor (D-A) systems has received considerable attention. We analyzed the fluctuations of interfacial PET from MAPbBr3 or CsPbBr3 PQDs to classical electron acceptors such as 7,7,8,8-tetracyanoquinodimethane (TCNQ) and 1,2,4,5-tetracyanobenzene (TCNB) at single-particle and ensemble levels. The significantly negative Gibbs free energy changes of PET estimated from the donor-acceptor redox potentials, the donor-acceptor sizes, and the solvent dielectric properties help us clarify the PET in the above D-A systems. The dynamic nature of PET is apparent from the decrease in photoluminescence (PL) lifetimes and PL photocounts of PQDs with an increase in the acceptor concentrations. Also, the acceptor radical anion spectrum helps us characterize the charge-separated states. Furthermore, the PL blinking time and PET rate fluctuations (108 to 107 s-1) provide us with single-molecule level information about interfacial PET in perovskites.
• Luminescent quantum dots: Synthesis, optical properties, bioimaging and toxicity.

  Jeladhara Sobhanan, Jose V Rival, Abdulaziz Anas, Edakkattuparambil Sidharth Shibu, Yuta Takano, Vasudevanpillai Biju

  Advanced drug delivery reviews 197 114830 - 114830 2023年04月20日 [査読有り]
   

  Luminescent nanomaterials such as semiconductor nanocrystals (NCs) and quantum dots (QDs) attract much attention to optical detectors, LEDs, photovoltaics, displays, biosensing, and bioimaging. These materials include metal chalcogenide QDs and metal halide perovskite NCs. Since the introduction of cadmium chalcogenide QDs to biolabeling and bioimaging, various metal nanoparticles (NPs), atomically precise metal nanoclusters, carbon QDs, graphene QDs, silicon QDs, and other chalcogenide QDs have been infiltrating the nano-bio interface as imaging and therapeutic agents. Nanobioconjugates prepared from luminescent QDs form a new class of imaging probes for cellular and in vivo imaging with single-molecule, super-resolution, and 3D resolutions. Surface modified and bioconjugated core-only and core-shell QDs of metal chalcogenides (MX; M = Cd/Pb/Hg/Ag, and X = S/Se/Te,), binary metal chalcogenides (MInX2; M = Cu/Ag, and X = S/Se/Te), indium compounds (InAs and InP), metal NPs (Ag, Au, and Pt), pure or mixed precision nanoclusters (Ag, Au, Pt), carbon nanomaterials (graphene QDs, graphene nanosheets, carbon NPs, and nanodiamond), silica NPs, silicon QDs, etc. have become prevalent in biosensing, bioimaging, and phototherapy. While heavy metal-based QDs are limited to in vitro bioanalysis or clinical testing due to their potential metal ion-induced toxicity, carbon (nanodiamond and graphene) and silicon QDs, gold and silica nanoparticles, and metal nanoclusters continue their in vivo voyage towards clinical imaging and therapeutic applications. This review summarizes the synthesis, chemical modifications, optical properties, and bioimaging applications of semiconductor QDs with particular references to metal chalcogenide QDs and bimetallic chalcogenide QDs. Also, this review highlights the toxicity and pharmacokinetics of QD bioconjugates.
• Halide Perovskite Single Crystals and Nanocrystal Films as Electron Donor-Acceptor Heterojunctions

  M. D. Shahjahan, Takuya Okamoto, Lata Chouhan, Bhagyashree Mahesha Sachith, Narayan Pradhan, Hiroaki Misawa, Vasudevanpillai Biju

  ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 2022年12月 [査読有り]
   

  Halide perovskites are materials for future optical displays and solar cells. Electron donor-acceptor perovskite heterostructures with distinguishing halide compositions are promising for transporting and harvesting photogenerated charge carriers. Combined e-beam lithography and anion exchange are promising to develop such heterostructures but challenging to prepare multiple heterojunctions at desired locations in single crystals. We demonstrate swift laser trapping-assisted band gap engineering at the desired locations in MAPbBr(3) microrods, microplates, or nanocrystal thin films. The built-in donor-acceptor double and multi-heterojunction structures let us transport and trap photogenerated charge carriers from wide-band gap bromide to narrow-band gap iodide domains. We discuss the charge carrier transport and trapping mechanisms from the viewpoints of engineered bands and band continuity. This work offers a convenient method for designing single-, double- and multi-heterojunction donor-acceptor halide perovskites for photovoltaic, photonic, and electronic applications.
• Caging and photo-triggered uncaging of singlet oxygen by excited state engineering of electron donor–acceptor-linked molecular sensors

  Devika Sasikumar, Yuta Takano, Hanjun Zhao, Reiko Kohara, Morihiko Hamada, Yasuhiro Kobori, Vasudevanpillai Biju

  Scientific Reports 12 1 2022年12月 [査読有り]
   

  Abstract Singlet oxygen (¹O₂), one of the most sought-after species in oxidative chemical reactions and photodynamic cancer therapy, is activated and neutralized in the atmosphere and living cells. It is essential to see "when" and "where" ¹O₂ is produced and delivered to understand and utilize it. There is an increasing demand for molecular sensor tools to capture, store, and supply ¹O₂, controlled by light and engineered singlet and triplet states, indicating the ¹O₂-capturing-releasing state. Here, we demonstrate the outstanding potential of an aminocoumarin-methylanthracene-based electron donor–acceptor molecule (1). Spectroscopic measurements confirm the formation of an endoperoxide (1-O₂) which is not strongly fluorescent and remarkably different from previously reported ¹O₂ sensor molecules. Moreover, the photoexcitation on the dye in 1-O₂ triggers fluorescence enhancement by the oxidative rearrangement and a competing ¹O₂ release. The unique ability of 1 will pave the way for the spatially and temporally controlled utilization of ¹O₂ in various areas such as chemical reactions and phototherapies.
• Photoeradication of aquatic pathogens by curcumin for clean and safe drinking water

  Sulfiya K. Moideen, Abdulaziz Anas, Jeladhara Sobhanan, Hanjun Zhao, Vasudevanpillai Biju

  Journal of Photochemistry and Photobiology A: Chemistry 432 114104 - 114104 2022年11月 [査読有り]
  
• Electroluminescence of Halide Perovskite Single Crystals Showing Stochastically Active Multiple Emitting Centers

  Sankaramangalam Balachandran Bhagyalakshmi, Dong Zhang, Vasudevanpillai Biju

  The Journal of Physical Chemistry C 126 42 17826 - 17835 2022年10月17日 [査読有り]
  
• Excitation‐Wavelength‐dependent Functionalities of Temporally‐controlled Sensing and Generation of Singlet Oxygen by a Photoexcited State Engineered Rhodamine 6G‐anthracene Conjugate

  Hanjun Zhao, Yuta Takano, Devika Sasikumar, Yukiko Miyatake, Vasudevanpillai Biju

  Chemistry – A European Journal 2022年10月12日 [査読有り]
   

  The present study provides design guidance for unique multipotent molecules that sense and generate singlet oxygen (O-1(2)). A rhodamine 6G-aminomethylanthracene-linked donor-acceptor molecule (RA) is designed and synthesized for demonstrating wavelength-dependent functionalities as follows; (i) RA acts as a conventional fluorogenic O-1(2) sensor molecule like the commercially available reagent, singlet oxygen sensor green (SOSG), when it absorbs ultraviolet (UV)-visible light and reacts with O-1(2). (ii) RA acts as a temporally controlled O-1(2) sensing reagent under the longer wavelength (similar to 700 nm) photosensitization. RA enters an intermediate state after capturing O-1(2) and does not become strongly fluorescent until it is exposed to UV, blue, or green light. (iii) RA acts as an efficient photosensitizer to generate O-1(2) under green light illumination. The spin-orbit charge transfer mediated intersystem crossing (SOCT-ISC) process achieves this function, and RA shows a potential cancer-killing effect on pancreatic cancer cells. The wavelength-switchable functionalities in RA offer to promise molecular tools to apply O-1(2) in a spatiotemporal manner.
• Inorganic Chain Mediated Excitonic Properties in One-Dimensional Lead Halide Hybrid Perovskites

  Chen Xue, Hengming Huang, Sadafumi Nishihara, Vasudevanpillai Biju, Xiao-ming Ren, Takayoshi Nakamura

  The Journal of Physical Chemistry Letters 13 32 7405 - 7412 2022年08月18日 [査読有り]
  
• Multimodal CTC detection using stem cell antigen-specific immunosilica particles and immunofluorescent quantum dots

  Jeladhara Sobhanan, Yuta Takano, Sakiko Sugino, Eri Hirata, Shohei Yamamura, Vasudevanpillai Biju

  NPG ASIA MATERIALS 14 1 2022年01月 [査読有り]
   

  Amid the COVID-19 pandemic, cancer continues to be the most devastating disease worldwide. Liquid biopsy of circulating tumor cells (CTCs) has recently become a painless and noninvasive tool for obtaining carcinoma cell samples for molecular profiling. Here, we report efficient detection and collection of cancer cells in blood samples by combining stem cell antigen (CD44)-specific immunosilica particles and immunofluorescent quantum dots with spectrally and temporally resolved single-photon counting. We accurately detect 1-10 cells among 100 cancer cells of the breast, lungs, or cervix in 1 mL blood samples. In addition, the bright and narrowband emission of CdSe/ZnS quantum dots enables temporally and spectrally resolved photon counting for multiplexed cancer cell detection. The cancer cell-specific and large immunosilica particles helped us collect the specific cells. We validate the detection efficiency and multimodality of this strategy by time-stamped and energy-dispersed single-photon counting of orange- and red-emitting quantum dots and green-fluorescing nuclei stained with Syto-13/25 dye. Thus, the present work highlights the prospects of multimodal CTC detection for noninvasive cancer screening and postsurgical or therapeutic follow-up.
• Mechano-optical Modulation of Excitons and Carrier Recombination in Self-Assembled Halide Perovskite Quantum Dots

  Zhijing Zhang, Sushant Ghimire, Takuya Okamoto, Bhagyashree Mahesha Sachith, Jeladhara Sobhanan, Challapalli Subrahmanyam, Vasudevanpillai Biju

  ACS NANO 2022年01月 [査読有り]
   

  Mechanically modulating optical properties of semiconductor nanocrystals and organic molecules are valuable for mechano-optical and optomechanical devices. Halide perovskites with excellent optical and electronic properties are promising for such applications. We report the mechanically changing excitons and photoluminescence of self-assembled formamidinium lead bromide (FAPbBr(3)) quantum dots. The as-synthesized quantum dots (3.6 nm diameter), showing blue emission and a short photoluminescence lifetime (2.6 ns), form 20-300 nm 2D and 3D self-assemblies with intense green emission in a solution or a film. The blue emission and short photoluminescence lifetime of the quantum dots are different from the delayed (ca. 550 ns) green emission from the assemblies. Thus, we consider the structure and excitonic properties of individual quantum dots differently from the self-assemblies. The blue emission and short lifetime of individual quantum dots are consistent with a weak dielectric screening of excitons or strong quantum confinement. The red-shifted emission and a long photoluminescence lifetime of the assemblies suggest a strong dielectric screening that weakens the quantum confinement, allowing excitons to split into free carriers, diffuse, and trap. The delayed emission suggests nongeminate recombination of diffusing and detrapped carriers. Interestingly, the green emission of the self-assembly blueshifts by applying a lateral mechanical force (ca. 4.65 N). Correspondingly, the photoluminescence lifetime decreases by 1 order of magnitude. These photoluminescence changes suggest the mechanical dissociation of the quantum dot self-assemblies and mechanically controlled exciton splitting and recombination. The mechanically changing emission color and lifetime of halide perovskite are promising for mechano-optical and optomechanical switches and sensors.
• Molecular recognition in the infection, replication, and transmission of COVID-19-causing SARS-CoV-2: an emerging interface of infectious disease, biological chemistry, and nanoscience

  Prem Kumar, Jeladhara Sobhanan, Yuta Takano, Vasudevanpillai Biju

  NPG Asia Materials 13 1 2021年12月 [査読有り]
   

  A coronavirus (CoV) commonly known as SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) and causing COVID-19 (coronavirus disease of 2019) has become a pandemic following an outbreak in Wuhan. Although mutations in the SARS-CoV-2 spike glycoprotein (SGP) are obvious from comparative genome studies, the novel infectious nature of the virus, its new varients detected in the UK, and outside and recovery–death ratios of COVID-19 inspired us to review the mechanisms of the infection, replication, release, and transmission of progeny virions and the immune response in the host cell. In addition to the specificity of SARS-CoV-2 binding to angiotensin-converting enzyme 2 receptor and transmembrane protease serine 2, the varied symptoms and severity of the infection by the original and mutated forms of the virus suggest the significance of correlating the host innate and adaptive immunity with the binding of the virus to the mannose receptor via lipopolysaccharides (LPSs), toll-like receptors via LPS/proteins/RNA, and sialic acid (Sia) via hemagglutinin, or sugar-acid segments of glycans. HA-to-Sia binding is considered based on the innate Sia N-acetylneuraminic acid and the acquired Sia N-glycolylneuraminic acid in the epithelial cells and the sialidase/neuraminidase- or esterase-hydrolyzed release and transmission of CoVs. Furthermore, the cytokine storms common to aged humans infected with SARS-CoV-2 and aged macaques infected with SARS-CoV encourage us to articulate the mechanism by which the nuclear capsid protein and RNAs bypass the pattern recognition-induced secretion of interferons (IFNs), which stimulate IFN genes through the Janus-activated kinase-signal transducer and activator of a transcription pathway, leading to the secretion of antiviral proteins such as myxovirus resistance protein A/B. By considering the complexities of the structure, and the infectious nature of the virus and the structures and functions of the molecules involved in CoV infection, replication, and immune response, a new interface among virology, immunology, chemistry, imaging technology, drug delivery, and nanoscience is proposed and will be developed. This interface can be an essential platform for researchers, technologists, and physicians to collaborate and develop vaccines and medicines against COVID-19 and other pandemics in the future.
• Advances in photodynamic antimicrobial chemotherapy

  Abdulaziz Anas, Jeladhara Sobhanan, K.M. Sulfiya, C. Jasmin, P.K. Sreelakshmi, Vasudevanpillai Biju

  Journal of Photochemistry and Photobiology C: Photochemistry Reviews 49 100452 - 100452 2021年12月 [査読有り]
  
• Emerging Materials for Plasmon-assisted Photoelectrochemical Water Splitting

  Palyam Subramanyam, Bhagatram Meena, Vasudevanpillai Biju, Hiroaki Misawa, Subrahmanyam Challapalli

  Journal of Photochemistry and Photobiology C: Photochemistry Reviews 100472 - 100472 2021年11月 [査読有り]
  
• Long-Range Interfacial Charge Carrier Trapping in Halide Perovskite-C60 and Halide Perovskite-TiO2 Donor–Acceptor Films

  Bhagyashree Mahesha Sachith, Takuya Okamoto, Sushant Ghimire, Tomokazu Umeyama, Yuta Takano, Hiroshi Imahori, Vasudevanpillai Biju

  The Journal of Physical Chemistry Letters 12 35 8644 - 8651 2021年09月09日 [査読有り]
   

  Interfacial electron transfer across perovskite-electron acceptor heterojunctions plays a significant role in the power-conversion efficiency of perovskite solar cells. Thus, electron donor-acceptor thin films of halide perovskite nanocrystals receive considerable attention. Nevertheless, understanding and optimizing distance- and thickness-dependent electron transfer in perovskite-electron acceptor heterojunctions are important. We reveal the distance-dependent and diffusion-controlled interfacial electron transfer across donor-acceptor heterojunction films formed by formamidinium or cesium lead bromide (FAPbBr(3)/CsPbBr3) perovskite nanocrystals with TiO2/C-60. Self-assembled nanocrystal films prepared from FAPbBr(3) show a longer photoluminescence lifetime than a solution, showing a long-range carrier migration. The acceptors quench the photoluminescence intensity but not the lifetime in a solution, revealing a static electron transfer. Conversely, the electron transfer in the films changes from dynamic to static by moving toward the donor-acceptor interface. While radiative recombination dominates the electron transfer at 800 mu m or farther, the acceptors scavenge the photogenerated carriers within 100 mu m. This research highlights the significance of interfacial electron transfer in perovskite films.
• Efficient solar water splitting using a CdS quantum dot decorated TiO2/Ag2Se photoanode

  Bhagatram Meena, Palyam Subramanyam, Duvvuri Suryakala, Vasudevanpillai Biju, Challapalli Subrahmanyam

  International Journal of Hydrogen Energy 2021年08月 [査読有り]
  
• State of the Art and Prospects for Halide Perovskite Nanocrystals

  Amrita Dey, Junzhi Ye, Apurba De, Elke Debroye, Seung Kyun Ha, Eva Bladt, Anuraj S. Kshirsagar, Ziyu Wang, Jun Yin, Yue Wang, Li Na Quan, Fei Yan, Mengyu Gao, Xiaoming Li, Javad Shamsi, Tushar Debnath, Muhan Cao, Manuel A. Scheel, Sudhir Kumar, Julian A. Steele, Marina Gerhard, Lata Chouhan, Ke Xu, Xian-gang Wu, Yanxiu Li, Yangning Zhang, Anirban Dutta, Chuang Han, Ilka Vincon, Andrey L. Rogach, Angshuman Nag, Anunay Samanta, Brian A. Korgel, Chih-Jen Shih, Daniel R. Gamelin, Dong Hee Son, Haibo Zeng, Haizheng Zhong, Handong Sun, Hilmi Volkan Demir, Ivan G. Scheblykin, Iván Mora-Seró, Jacek K. Stolarczyk, Jin Z. Zhang, Jochen Feldmann, Johan Hofkens, Joseph M. Luther, Julia Pérez-Prieto, Liang Li, Liberato Manna, Maryna I. Bodnarchuk, Maksym V. Kovalenko, Maarten B. J. Roeffaers, Narayan Pradhan, Omar F. Mohammed, Osman M. Bakr, Peidong Yang, Peter Müller-Buschbaum, Prashant V. Kamat, Qiaoliang Bao, Qiao Zhang, Roman Krahne, Raquel E. Galian, Samuel D. Stranks, Sara Bals, Vasudevanpillai Biju, William A. Tisdale, Yong Yan, Robert L. Z. Hoye, Lakshminarayana Polavarapu

  ACS Nano 15 7 10775 - 10981 2021年07月27日 [査読有り]
  
• Shape‐Dependent Kinetics of Halide Vacancy Filling in Organolead Halide Perovskites

  Takuya Okamoto, Md. Shahjahan, Vasudevanpillai Biju

  Advanced Optical Materials 2100355 - 2100355 2021年06月18日 [査読有り]
   

  Halide perovskites show high photoluminescence quantum yields and tunable bandgap. While perovskites' optical properties significantly degrade due to the ionic and electronic defects, a correlation among their structure, size, defects, and degradation rate remains concealed. The authors report the crystal shape- and halide vacancy-dependent stability of methylammonium lead bromide single crystals. The vacancies are filled in the cubic-, plate-, and rod-shaped crystals by the halide-soaking and light-soaking processes. The differences in the stability, photoluminescence intensity, lifetime, and vacancy filling rates in these geometrical shapes derive from their specific surface-to-volume ratios. The shape-dependent vacancy filling helps to correlate the electron microscope images, elemental compositions, and the photoluminescence intensity and lifetime.
• Real-Time Blinking Suppression of Perovskite Quantum Dots by Halide Vacancy Filling

  Lata Chouhan, Syoji Ito, Elizabeth Mariam Thomas, Yuta Takano, Sushant Ghimire, Hiroshi Miyasaka, Vasudevanpillai Biju

  ACS Nano 15 2 2831 - 2838 2021年02月23日 [査読有り]
   

  Despite the excellent optoelectronic properties of halide perovskites, the ionic and electronic defects adversely affect the stability and durability of perovskites and their devices. These defects, intrinsic or produced by environmental factors such as oxygen, moisture, or light, not only cause chemical reactions that disintegrate the structure and properties of perovskites but also induce undesired photoluminescence blinking to perovskite quantum dots and nanocrystals. Blinking is also caused by the nonradiative Auger processes in the photocharged quantum dots or nanocrystals. Herein, we find real-time suppression of halide vacancy-assisted nonradiative exciton recombination and photoluminescence blinking in MAPbBr3 and MAPbI3 perovskite quantum dots by filling the vacancies using halide precursors (MABr and MAI). Also, halide vacancy filling increases the photoluminescence quantum efficiencies and lifetimes of the quantum dots. We estimate the rates of halide vacancy-assisted nonradiative recombination at 1 × 108 s-1 for MAPbBr3 and 1.9 × 109 s-1 for MAPbI3 quantum dots. The real-time blinking suppression using the halide precursors and statistical analysis of the ON/OFF blinking time reveal that the halide vacancies contribute to the type-A blinking through charging and discharging. Conversely, the blinking of the quantum dots after halide vacancy filling is dominated by the type-B mechanism.
• Heterojunction Perovskite Microrods Prepared by Remote‐Controlled Vacancy Filling and Halide Exchange

  Md Shahjahan, Ken‐ichi Yuyama, Takuya Okamoto, Vasudevanpillai Biju

  Advanced Materials Technologies 6 2 2000934 - 2000934 2021年02月 [査読有り]
   

  Anion exchange reaction tunes the band gap of halide perovskites, which proceeds by the migration of the ions through the halide vacancies. This study reports the preparation of the heterojunction perovskite microrods by optically controlled localized halide vacancy filling, and halide exchange leading to color tuning in the MAPbBr(3) microrod crystals. The exchange reaction is homogeneously suppressed by treating the crystal with a halide precursor solution, whereas the reaction is locally inhibited at the specific site of a crystal by filling the halide vacancies using a tightly focused beam of a near-infrared laser. By controlling the density of halide vacancies at the specific site of the crystal, the rate of nonradiative recombination of charge carriers in the crystal is controlled. This halide vacancy filling by the remote-controlled reaction helps to locally control the crystal quality and photoluminescence for designing perovskite-based high-quality photovoltaic and optoelectronic devices.
• Photoluminescence investigations of sulfur quantum dots synthesized by a bubbling-assisted strategy

  Shuo Liu, Henggang Wang, Anrui Feng, Jianyu Chang, Chuanchuan Zhang, Yu-e Shi, Yongqing Zhai, Vasudevanpillai Biju, Zhenguang Wang

  Nanoscale Advances 3 14 4271 - 4275 2021年 

  The photoluminescence mechanisms of S-dots were revealed by the bubbling-assisted synthesis and spectroscopic study. The emission color of the S-dots depends on the size, and the emission efficiency is affected by the surface sulfur species.

• Photoluminescent Ozone Sensor with Enhanced Sensitivity by Using CdSe/ZnS Quantum Dots Modified with Gold and Platinum

  Masanori ANDO, Kosuke INAGAKI, Hideya KAWASAKI, Vasudevanpillai BIJU, Yasushi SHIGERI

  Analytical Sciences 36 8 989 - 995 2020年08月10日 

  We report photoluminescence-based ozone sensing using composite films composed of gold or platinum and red-emitting CdSe/ZnS core-shell quantum dots. The sensing efficiency of quantum dots is enhanced by the addition of noble metals. The composite films undergo reversible changes in photoluminescence intensity (measured at excitation/emission wavelengths of 365/652 - 659 nm) in the presence of ppm levels of ozone in air at 25°C and at atmospheric pressure. The sensitivity of the composite films does not saturate with ozone in the 0.5 - 200 ppm concentration range. When compared with a quantum dot-only film, the composite films show higher sensitivities to 0.5 ppm ozone of 27% (gold) and 43% (platinum). When compared with a quantum dot-only film, the photoluminescence of the gold- or platinum-palladium alloy-based film recovers faster after the removal of ozone in the surrounding atmosphere. Thus, platinum- or gold-conjugated quantum-dot films form sensor modules for the reversible and highly sensitive detection of ozone under the tested ambient conditions.
• Spatio-temporally-controlled synthesis of lead halide perovskite crystals by laser trapping

  Ken-ichi Yuyama, Islam Md Jahidul, Vasudevanpillai Biju

  Optical Manipulation and Structured Materials Conference 2020 2020年06月15日
• 光増感分子rTPAを搭載したミトコンドリア標的型ナノカプセルの構築および担癌モデルマウスを用いた癌光治療戦略の検証

  山田 勇磨, Satrialdi, 高野 勇太, Biju Vasudevanpillai, 原島 秀吉

  日本薬学会年会要旨集 140年会 26X - am11 (公社)日本薬学会 2020年03月
• Remote tuning of bandgap and emission of lead perovskites by spatially controlled halide exchange reactions

  Md Jahidul Islam, Md Shahjahan, Ken-ichi Yuyama, Vasudevanpillai Biju

  ACS Materials Letters 2 4 403 - 408 2020年02月 [査読有り][通常論文]
  
• The Confinement and Migration of Charge-Carriers in Lead Halide Perovskites

  Sushant Ghimire, Lata Chouhan, Vasudevanpillai Biju

  Photosynergetic Responses in Molecules and Molecular Aggregates 197 - 210 2020年
• SPR induced photoluminescne quenching in Quantum MAPbBr3 -QD/TiO2 inteface

  Katta Venkata Seshaiah, Lata Chouhan, Vasudevanpillai Biju, Sai Santhosh Kumar Raavi

  OSA Advanced Photonics Congress (AP) 2020 (IPR, NP, NOMA, Networks, PVLED, PSC, SPPCom, SOF) 2020年
• Synthesis, optoelectronic properties and applications of halide perovskites

  Lata Chouhan, Sushant Ghimire, Challapalli Subrahmanyam, Tsutomu Miyasaka, Vasudevanpillai Biju

  Chemical Society Reviews 49 10 2869 - 2885 2020年 [査読有り]
   

  Halide perovskites have emerged as a class of most promising and cost-effective semiconductor materials for next generation photoluminescent, electroluminescent and photovoltaic devices.

• Toxicity of nanomaterials due to photochemical degradation and the release of heavy metal ions

  Jeladhara Sobhanan, Philip Jones, Reiko Kohara, Sakiko Sugino, Martin Vacha, Challapally Subrahmanyam, Yuta Takano, Fred Lacy, Vasudevanpillai Biju

  Nanoscale 12 43 22049 - 22058 2020年 [査読有り]
   

  The cytotoxicity and genotoxicity of PbS quantum dots by photochemical etching and the release of lead ions.

• Near-infrared light control of membrane potential by an electron donor–acceptor linked molecule

  Yuta Takano, Kazuaki Miyake, Jeladhara Sobhanan, Vasudevanpillai Biju, Nikolai V. Tkachenko, Hiroshi Imahori

  Chemical Communications 56 83 12562 - 12565 2020年 [査読有り]
   

  (π-Extended porphyrin)–fullerene linked molecules are synthesized to utilize the molecular excited states induced by near-infrared light. One of the molecules successfully alters the membrane potential.

• A photoanode with plasmonic nanoparticles of earth abundant bismuth for photoelectrochemical reactions

  Palyam Subramanyam, Melepurath Deepa, Sai Santosh Kumar Raavi, Hiroaki Misawa, Vasudevanpillai Biju, Challapalli Subrahmanyam

  Nanoscale Advances 2 12 5591 - 5599 2020年 [査読有り]
   

  A wide range of technologies has been developed for producing hydrogen economically and in greener ways.

• Extinction of Antimicrobial Resistant Pathogens Using Silver Embedded Silica Nanoparticles and an Efflux Pump Blocker

  Jiya Jose, Abdulaziz Anas, Bina Jose, Anand B. Puthirath, Sujith Athiyanathil, Chekidhenkuzhiyil Jasmin, M. R. Anantharaman, Shanta Nair, Challapalli Subrahmanyam, Vasudevanpillai Biju

  ACS Applied Bio Materials 2 11 4681 - 4686 2019年11月18日
• Mixed-halide perovskite synthesis by chemical reaction and crystal nucleation under an optical potential

  Md Jahidul Islam, Ken-ichi Yuyama, Kiyonori Takahashi, Takayoshi Nakamura, Katsuaki Konishi, Vasudevanpillai Biju

  NPG Asia Materials 11 31  2019年06月 [査読有り][通常論文]
   

  The development of new methods to engineer lead halide perovskite crystals with a controlled band gap and emission properties is an active subject in materials science and chemistry. We present the preparation of mixed-halide lead perovskites by spatially- and temporally- controlled chemical reactions and crystal growth under an optical potential in unsaturated precursor solutions. The crystals are characterized by transmission and photoluminescence spectral measurements and X-ray diffraction analysis. When compared with the spontaneous formation of multiple crystals in saturated precursor solutions, the optical potential creates large single crystals with a high chloride composition, providing distinct blue and green fluorescent crystals of chloride-bromide lead perovskites. We discuss the formation of mixed-halide perovskites from the viewpoints of an increased rate of chemical reaction via the formation and desolvation of precursor complexes and a decreased free energy potential.
• Blinking Beats Bleaching: The Control of Superoxide Generation by Photo‐ionized Perovskite Nanocrystals

  Lata Chouhan, Sushant Ghimire, Vasudevanpillai Biju

  Angewandte Chemie International Edition 58 15 4875 - 4879 2019年04月
• Photoinduced Photoluminescence Enhancement in Self-assembled Clusters of Formamidinium Lead Bromide Perovskite Nanocrystals

  Sushant Ghimire, Vijayakumar C Nair, Chinnadurai Muthu, Ken-ichi Yuyama, Martin Vacha, Vasudevanpillai Biju

  Nanoscale 11 19 9335 - 9340 2019年03月 [査読有り][通常論文]
   

  Delayed recombination of photogenerated charge carriers or excitons is accomplished in self-assemblies of perovskite nanocrystals.

• Phase transfer reaction for the preparation of stable polymer-quantum dot conjugates

  Geethy P Gopalan, Ajith Nair Anil, Sushant Ghimire, Nidhin Joy, Ken-ichi Yuyama, Vasudevanpillai Biju, Raju Francis

  Journal of Photochemistry and Photobiology A: Chemistry 371 91 - 97 2019年02月 [査読有り][通常論文]
  
• The optimization of cancer photodynamic therapy by utilization of a pi-extended porphyrin-type photosensitizer in combination with MITO-Porter

  Satrialdi, Reina Munechika, Vasudevanpillai Biju, Yuta Takano, Hideyoshi Harashima, Yuma Yamada

  Chemical Communications 2019年 [査読有り][通常論文]
  
• Photoinduced Betaine Generation for the Efficient Photothermal Energy Conversion

  Devika Sasikumar, Yuta Takano, Vasudevanpillai Biju

  Chemistry A European Journal 2019年 [査読有り][通常論文]
  
• Nonradiative Energy Transfer through Distributed Bands in Piezochemically-synthesized Cesium and Formamidinium Lead Halide Perovskites

  Sankaramangalam Balachandran Bhagyalakshmi, Sushant Ghimire, Kiyonari Takahashi, Ken-ichi Yuyama, Yuta Takano, Takayoshi Nakamura, Vasudevan Biju

  Chemistry A European Journal 26 10 2133 - 2137 2019年 [査読有り][通常論文]
  
• Photon-recycling by Energy Transfer in Piezochemically Synthesized and Close-packed Methyl Ammonium Lead Halide Perovskites

  Sushant Ghimire, Kiyonori Takahashi, Yuta Takano, Takayoshi Nakamura, Vasudevanpillai Biju

  Journal of Physical Chemistry C 123 45 27752 - 27758 2019年 [査読有り][通常論文]
   

  Photon recycling by multiple reabsorption-emission is responsible for the long-range energy transport in large crystals and thick films of lead halide perovskites, resulting in red-shifted and delayed emission. Apart from such a radiative process, nonradiative energy transfer influences photon recycling in perovskites with close-packed donor-acceptor-type states. In this study, we report the role of nonradiative energy transfer on photon recycling in piezochemically synthesized and close-packed pure and mixed halide methylammonium lead perovskites. Here, the pressure applied to precursors of perovskites helps us to synthesize and close-pack perovskite crystallites into pellets. Nonetheless, interestingly, we find that the applied pressure redistributes the emission maxima or band- gap of these perovskites. The temporally and spectrally resolved photoluminescence from the mixed halide sample unveils nonradiative energy transfer from a higher (bromide) to a lower (iodide) band-gap domain, where the rate of relaxation of the bromide domain is higher than that of the pure bromide perovskite. These results help us to confirm the role of nonradiative energy transfer on photon recycling in perovskites.
• Kinetics of singlet oxygen sensing using 9-substituted anthracene derivatives #

  Devika Sasikumar, Reiko Kohara, Yuta Takano, Ken-ichi Yuyama, Vasudevanpillai Biju

  Journal of Chemical Sciences 131 1 5 - 5 2019年01月 [査読有り][通常論文]
  
• Stark Effect and Environment Induced Modulation of Emission in Single Halide Perovskite Nanocrystals

  Dharmendar Kumar Sharma, Shuzo Hirata, Vasudevanpillai Biju, Martin Vacha

  ACS nano 13 1 624 - 632 2019年01月 [査読有り][通常論文]
   

  Organic-inorganic halide perovskites have emerged as promising materials for next-generation solar cells. In nanostructured form also, these materials are excellent candidates for optoelectronic applications such as lasers and light-emitting diodes for displays and lighting. While great progress has been achieved so far in optimizing the intrinsic photophysical properties of perovskite nanocrystals (NCs), in working optoelectronic devices, external factors, such as the effects of conducting environment and the applied electric field on exciton generation and photon emission, have been largely unexplored. Here, we use NCs of the all-inorganic perovskite CsPbBr3 dispersed polyvinyl carbazole, a hole-conductor, and in poly(methyl methacrylate), an insulator, to examine the effects of applied electric field and conductivity of the matrix on the perovskite photophysics at the single-particle level. We found that the conducting environment causes a significant decrease of photoluminescence (PL) brightness of individual NCs due the appearance of intermediate-intensity emitting states with significantly shortened lifetime. Applied electric field has a similar effect and, in addition, causes a nonlinear spectral shift of the PL maxima, a combination of linear and quadratic Stark effects caused by environment-induced polarity and field-related polarizability. The environment and electric-field effects are explained by ionization of the NCs through hole transfer and emission of the resulting negatively charged excitons.
• Amplified and Multicolor Emission from Films and Interfacial Layers of Lead Halide Perovskite Nanocrystals

  Sushant Ghimire, Lata Chouhan, Yuta Takano, Kiyonori Takahashi, Takayoshi Nakamura, Vasudevan Pillai Biju, Kenichi Yuyama

  ACS Energy Letters 2018年11月 [査読有り][通常論文]
  
• Excitons and Biexciton Dynamics in Single CsPbBr3 Perovskite Quantum Dots

  Bin Li,He Huang, Guofeng Zhang, Changgang Yang, Wenli Guo, Ruiyun Chen, Qin Chengbing, Yan Gao, Vasudevan Pillai Biju, Andrey L Rogach, Liantuan Xiao, Suotang Jia

  The journal of physical chemistry letters 9 6934 - 6940 2018年11月 [査読有り][通常論文]
  
• Crystallization of Methylammonium Lead Halide Perovskites by Optical Trapping

  Vasudevan BIJU, Ken-ichi Yuyama, Md Jahidul Islam, Kiyonori Takahashi, Takayoshi Nakamura

  Angewandte Chemie 2018年08月 [査読有り][通常論文]
  
• Blinking Suppression in Highly-Excited CdSe/ZnS Quantum Dots by Electron Transfer under Large Positive Gibbs (Free) Energy Change

  Elizabeth Mariam Thomas, Sushant Ghimire, Reiko Kohara, Ajith Nair Anil, Ken-ichi Yuyama, Yuta Takano, K George Thomas, Vasudevan Pillai Biju

  ACS nano 12 9 9060 - 9069 2018年08月 [査読有り][通常論文]
  
• Quantum dot-polymer conjugates for stable luminescent displays

  Ghimire Sushant, Sivadas Anjaly, Yuyama Ken-ichi, Takano Yuta, Francis Raju, Biju Vasudevanpillai

  NANOSCALE 10 28 13368 - 13374 2018年07月28日 [査読有り][通常論文]
   

  The broad absorption of light in the UV-Vis-NIR region and the size-based tunable photoluminescence color of semiconductor quantum dots make these tiny crystals one of the most attractive antennae in solar cells and phosphors in electrooptical devices.

• Quantum dot–polymer conjugates for stable luminescent displays

  S Ghimire, A Sivadas, K Yuyama, Y Takano, R Francis, V Biju

  Nanoscale 10 28 13368 - 13374 2018年04月 [査読有り][通常論文]
   

  The broad absorption of light in the UV-Vis-NIR region and the size-based tunable photoluminescence color of semiconductor quantum dots make these tiny crystals one of the most attractive antennae in solar cells and phosphors in electrooptical devices.

• Relations of exciton dynamics in quantum dots to photoluminescence, lasing, and energy harvesting

  Sushant Ghimire, Vasudevanpillai Biju

  Journal of Photochemistry and Photobiology C: Photochemistry Reviews 34 137 - 151 2018年03月01日 [査読有り][通常論文]
   

  For the past three decades, the field of quantum dot research has been expanding enormously, owing to the unique dynamics of charge carriers in these tiny crystals. This review provides an overview of charge carrier dynamics in photoactivated quantum dots. Specifically, it deals with the exciton fine structure, multiple exciton generation and the origin and control of photoluminescence intermittency in cadmium and lead chalcogenide quantum dots. These properties are discussed within the framework of spectroscopy and microscopy of single and multiple exciton states. Finally, this review touches on the photoluminescence- and multiple exciton- based applications of quantum dots, such as lasing and high efficiency solar cells.
• Preface for special issue on photosynergetics

  Vasudevanpillai Biju, Tadashi Mori, Tsuyoshi Asahi, Hiroshi Miyasaka

  Journal of Photochemistry and Photobiology C: Photochemistry Reviews 34 1  2018年03月 [査読有り][通常論文]
  
• Relations of exciton dynamics in quantum dots to photoluminescence, lasing, and energy harvesting

  Sushant Ghimire, Vasudevanpillai Biju

  Journal of Photochemistry and Photobiology C: Photochemistry Reviews 34 137 - 151 2018年03月01日 [査読有り][通常論文]
   

  For the past three decades, the field of quantum dot research has been expanding enormously, owing to the unique dynamics of charge carriers in these tiny crystals. This review provides an overview of charge carrier dynamics in photoactivated quantum dots. Specifically, it deals with the exciton fine structure, multiple exciton generation and the origin and control of photoluminescence intermittency in cadmium and lead chalcogenide quantum dots. These properties are discussed within the framework of spectroscopy and microscopy of single and multiple exciton states. Finally, this review touches on the photoluminescence- and multiple exciton- based applications of quantum dots, such as lasing and high efficiency solar cells.
• Quantum Dot-Peptide Nanoassembly on Mesoporous Silica Nanoparticle for Biosensing

  Sreenadh Sasidharan Pillai, Hiroshi Yukawa, Daisuke Onoshima, Vasudevanpillai Biju, Yoshinobu Baba

  Nano Hybrids and Composites 19 55 - 72 2018年02月 [査読有り][通常論文]
  
• Development of technologies for sensing ozone in ambient air

  Masanori Ando, Vasudevanpillai Biju, Yasushi Shigeri

  Analytical Sciences 34 3 263 - 271 2018年 [査読有り][通常論文]
   

  Ozone (O3) gas is widely used as a strong oxidizing agent for many purposes, such as the decomposition/removal of organic contaminants and photoresist, and the deodorization/disinfection of air and water. However, ozone is highly toxic to the human body when the air concentration exceeds about 1 ppm. Therefore, there is increasing demand for simple, sensitive, reliable, and cost-effective techniques for sensing ozone gas. This article describes the features, advantages, and disadvantages of the available, practical techniques for sensing ozone gas in ambient air. The advantages of optical gas sensors as next-generation sensors is specifically introduced. The features of photoluminescent, semiconductor nanoparticles (quantum dots, QDs) as bright phosphors with the potential for various applications is further explored. Lastly, recent research results demonstrating the ozone sensitivity of photoluminescent CdSe-based core-shell quantum dots are presented. These results strongly suggest that optical ozone sensing using photoluminescent quantum dots is a promising technique.
• OS1.3 - Optical Ozone Sensing by Composite Films of Noble Metals and CdSe/ZnS Quantum Dots

  M. Ando, V. Biju, H. Kawasaki, Y. Shigeri

  Proceedings IMCS 2018 2018年
• Optical control of mitochondrial reductive reactions in living cells using an electron donor-acceptor linked molecule

  Yuta Takano, Reina Munechika, Vasudevanpillai Biju, Hideyoshi Harashima, Hiroshi Imahori, Yuma Yamada

  NANOSCALE 9 47 18690 - 18698 2017年12月 [査読有り][通常論文]
   

  It has been known for decades that intracellular redox reactions control various vital functions in living systems, which include the synthesis of biomolecules, the modulation of protein functions, and cell signaling. Although there have been several reports on the control of such functions using DNA and RNA, the non-invasive optical control of biological functions is an important ongoing challenge. In this study, a hybrid of an electron donor-acceptor linked molecule based on a ferrocene(Fc)-porphyrin(ZnP)-fullerene-(C-60) analogue and an elaborately designed nano-carrier, referred to herein as a MITO-Porter, resulted in a successful photoinduced intermolecular electron transfer reaction via the long-lived intramolecular charge separation, leading to site-specific reductive reactions in the mitochondria of living HeLa cells. A Fc-ZnP-C-60 linked molecule, 1-Oct, was designed and prepared for taking advantage of the unique photophysical properties with excellent efficiency (i.e. a long lifetime and a high quantum yield) for photoinduced charge separation. The targeted delivery of 1-Oct to mitochondria was accomplished by using a combination of the Fc-ZnP-C-60 molecule and a drug delivery nano-carrier, MITO-Porter, that was recently established by our group for intracellular cargo delivery. The successful delivery of 1-Oct by the MITO-Porter permitted the optically-controlled generation of O-2(-) in the mitochondria of HeLa cells and the following induction of apoptosis as a cell signalling response was observed in confocal laser microscopy experiments. The obtained results indicate the use of an electron donor-acceptor system such as this can be a promising tool for the non-invasive triggering of redox-coupled cellular activities in living systems.
• Optical control of mitochondrial reductive reactions in living cells using an electron donor–acceptor linked molecule

  Yuta Takano, Reina Munechika, Vasudevanpillai Biju, Hideyoshi Harashima, Hiroshi Imahori, Yuma Yamada

  Nanoscale 9 47 18690 - 18698 2017年12月 [査読有り][通常論文]
   

  It has been known for decades that intracellular redox reactions control various vital functions in living systems, which include the synthesis of biomolecules, the modulation of protein functions, and cell signaling. Although there have been several reports on the control of such functions using DNA and RNA, the non-invasive optical control of biological functions is an important ongoing challenge. In this study, a hybrid of an electron donor-acceptor linked molecule based on a ferrocene(Fc)-porphyrin(ZnP)-fullerene-(C-60) analogue and an elaborately designed nano-carrier, referred to herein as a MITO-Porter, resulted in a successful photoinduced intermolecular electron transfer reaction via the long-lived intramolecular charge separation, leading to site-specific reductive reactions in the mitochondria of living HeLa cells. A Fc-ZnP-C-60 linked molecule, 1-Oct, was designed and prepared for taking advantage of the unique photophysical properties with excellent efficiency (i.e. a long lifetime and a high quantum yield) for photoinduced charge separation. The targeted delivery of 1-Oct to mitochondria was accomplished by using a combination of the Fc-ZnP-C-60 molecule and a drug delivery nano-carrier, MITO-Porter, that was recently established by our group for intracellular cargo delivery. The successful delivery of 1-Oct by the MITO-Porter permitted the optically-controlled generation of O-2(-) in the mitochondria of HeLa cells and the following induction of apoptosis as a cell signalling response was observed in confocal laser microscopy experiments. The obtained results indicate the use of an electron donor-acceptor system such as this can be a promising tool for the non-invasive triggering of redox-coupled cellular activities in living systems.
• Blue-Emitting Electron-Donor/Acceptor Dyads for Naked-Eye Fluorescence Detection of Singlet Oxygen

  Kohara Reiko, Yuyama Ken-ichi, Shigeri Yasushi, Biju Vasudevanpillai

  CHEMPHOTOCHEM 1 7 298 - 298 2017年07月 [査読有り][通常論文]
   

  The front cover artwork is provided by the group of Prof. V. Biju at the Research Institute for Electronic Science, Hokkaido University (Japan). The image shows an electron-donor/acceptor molecular sensor that sensitively responds to UV light or singlet oxygen and emits intense blue light. The butterfly wings carry the sensor and its fluorescent reaction products, and the butterfly bodies represent solutions of products. Read the full text of the Article at 10.1002/cptc. 201700046.
• Reversible photoluminescence sensing of gaseous alkylamines using CdSe-based quantum dots

  Masanori Ando, Takuya Kamimura, Koichi Uegaki, Vasudevanpillai Biju, Jennifer T. Damasco Ty, Yasushi Shigeri

  SENSORS AND ACTUATORS B-CHEMICAL 246 1074 - 1079 2017年07月 [査読有り][通常論文]
   

  We report here a novel, sensitive detection method for gaseous amines (primary, secondary and tertiary) using thin films of CdSe-based core-shell type quantum dots (CdSe/ZnS and CdSeTe/ZnS) deposited on a glass substrate. The photoluminescence intensity of the quantum dot thin films rapidly decreased on exposure to amine gas in air, and it reversibly recovered after the atmosphere was changed back to air without amine gas. On the other hand, oxygen, nitrogen, argon, carbon dioxide, or hydrogen, all components of natural air, did not affect the photoluminescence intensity of the quantum dot thin films. Interestingly, the photoluminescence of quantum dot films showed higher sensitivity to n-alkylamines, such as hexylamine, when compared with bulky or branched molecules, such as diethylamine and triethylamine. Furthermore, thin films of green-emitting quantum dots showed higher sensitivity to amines when compared with red-emitting ones, which was attributed to the large surface-to-volume ratios of smaller quantum dots. The reversible, reproducible, and selective responses of CdSe-based core-shell type quantum dots to gaseous amines in air suggested that quantum dot thin films could be promising photoluminescence-based optical amine gas sensors. (C) 2017 Elsevier B.V. All rights reserved.
• Blue‐Emitting Electron‐Donor/Acceptor Dyads for Naked‐Eye Fluorescence Detection of Singlet Oxygen

  Reiko Kohara, Ken‐ichi Yuyama, Yasushi Shigeri, Vasudevanpillai Biju

  ChemPhotoChem 1 7 299 - 303 2017年07月 [査読有り][通常論文]
   

  Singlet oxygen (O-1(2)) and other reactive oxygen species receive great attention in chemistry and biology. Fluorescence sensing is one of the most promising and widely used techniques in the detection of O-1(2). Nonetheless, the selectivity and sensitivity of O-1(2) detection are highly depended on the structure, absorption band, stability and emission color of the fluorogenic sensor. We introduce novel and simple intramolecular electron donor-acceptor dyads that selectively and sensitively emit intense blue light in response to O-1(2). The systematic changes in the emission intensity of the sensors allow detection of O-1(2) by the naked-eye. Furthermore, the blue-shifted absorption and blue emission bands of the sensors ensure selective excitation of common photosensitizers using visible light. The sensors are synthesized by a simple and single-step reaction, which when combined with the exceptionally high stability of the sensors against visible-light irradiation, makes them promising tools for O-1(2) detection in chemistry, biochemistry, materials science and the life sciences.
• Influence of Zn on the photoluminescence of colloidal (AgIn)(x)Zn2(1-x) S-2 nanocrystals

  Dharmendar Kumar Sharma, Shuzo Hirata, Lukasz Bujak, Vasudevanpillai Biju, Tatsuya Kameyama, Marino Kishi, Tsukasa Torimoto, Martin Vacha

  PHYSICAL CHEMISTRY CHEMICAL PHYSICS 19 5 3963 - 3969 2017年02月 [査読有り][通常論文]
   

  We study the effect of Zn on the photophysical properties of a family of group I-III-VI nanocrystals (NCs), namely in solid solutions of (AgIn)(x)Zn2(1-x)S2 (ZAIS). We focus on the comparison of the photo-luminescence (PL) properties of ZAIS NCs of comparable sizes and different amounts of Zn. This approach helps us to decouple the effects of size and varying chemical composition of the NCs which both influence the PL properties. We show that in the presence of Zn new radiative centers are generated which improve the NC quality in terms of PL quantum yield. However, an amount of Zn beyond a particular limit places the radiative recombination centers close to each other, leading to undesired interactions among charge carriers and non-radiative transitions. Proximity between the energy levels of these radiative centers and the conduction band leads to non-radiative localized-delocalized transitions, as evidenced from temperature dependent absorption, PL and lifetime measurements.
• Forster Resonance Energy Transfer Mediated Photoluminescence Quenching in Stoichiometrically Assembled CdSe/ZnS Quantum Dot-Peptide Labeled Black Hole Quencher Conjugates for Matrix Metalloproteinase-2 Sensing

  Sreenadh Sasidharan Pillavi, Hiroshi Yukawa, Daisuke Onoshima, Vasudevanpillai Biju, Yoshinobu Baba

  ANALYTICAL SCIENCES 33 2 137 - 142 2017年02月 [査読有り][通常論文]
   

  The steady state and time-resolved photoluminescence quenching of streptavidin modified CdSe/ZnS quantum dots (QDs) instigated by biotin-peptide-BHQ-1 (biotin-pep-BHQ-1) molecule was investigated. Here, we have achieved an efficient photoluminescence (PL) quenching of QDs with the conjugation of dark quencher (black hole quencher-BHQ) molecules intermediated with the GPLGVRGK peptide. The luminescence of streptavidin-QDs585 was decreased upon titration with a nano molar concentration of the biotin-GPLGVRGK-BHQ-1 molecule. It has been suggested that the decrease of QDs PL occurred through a Forster resonance energy transfer (FRET) mechanism from the analysis of steady state photoluminescence intensity measurements as well as time resolved lifetime measurements of streptavidin-QDs and QDs(pep-BHQ-1)(n) conjugates. The sequence of intermediate peptide GPLG down arrow VRGK can act as a target material for matrix metalloproteinases-2 (MMP-2) produced by cancer cells at its Gly and Val region, shown by the down-headed arrow. Interestingly, here the reported self-assembled QDs-(pep-BHQ-1)(n) conjugates could detect the presence MMP-2 at a detection limit of 1 ng/mL with a clear luminescence recovery.
• Influence of Zn on the photoluminescence of colloidal (AgIn) x Zn 2 (1− x) S 2 nanocrystals

  Dharmendar Kumar Sharma, Shuzo Hirata, Lukasz Bujak, Vasudevanpillai Biju, Tatsuya Kameyama, Marino Kishi, Tsukasa Torimoto, Martin Vacha

  Physical Chemistry Chemical Physics 19 5 3963 - 3969 2017年02月 [査読有り][通常論文]
   

  We study the effect of Zn on the photophysical properties of a family of group I-III-VI nanocrystals (NCs), namely in solid solutions of (AgIn)(x)Zn2(1-x)S2 (ZAIS). We focus on the comparison of the photo-luminescence (PL) properties of ZAIS NCs of comparable sizes and different amounts of Zn. This approach helps us to decouple the effects of size and varying chemical composition of the NCs which both influence the PL properties. We show that in the presence of Zn new radiative centers are generated which improve the NC quality in terms of PL quantum yield. However, an amount of Zn beyond a particular limit places the radiative recombination centers close to each other, leading to undesired interactions among charge carriers and non-radiative transitions. Proximity between the energy levels of these radiative centers and the conduction band leads to non-radiative localized-delocalized transitions, as evidenced from temperature dependent absorption, PL and lifetime measurements.
• Förster Resonance Energy Transfer Mediated Photoluminescence Quenching in Stoichiometrically Assembled CdSe/ZnS Quantum Dot-Peptide Labeled Black Hole Quencher Conjugates for Matrix Metalloproteinase-2 Sensing

  Sreenadh Sasidharan PILLAI, Hiroshi YUKAWA, Daisuke ONOSHIMA, Vasudevanpillai BIJU, Yoshinobu BABA

  Analytical Sciences 33 2 137 - 142 2017年02月 [査読有り][通常論文]
   

  The steady state and time-resolved photoluminescence quenching of streptavidin modified CdSe/ZnS quantum dots (QDs) instigated by biotin-peptide-BHQ-1 (biotin-pep-BHQ-1) molecule was investigated. Here, we have achieved an efficient photoluminescence (PL) quenching of QDs with the conjugation of dark quencher (black hole quencher-BHQ) molecules intermediated with the GPLGVRGK peptide. The luminescence of streptavidin-QDs585 was decreased upon titration with a nano molar concentration of the biotin-GPLGVRGK-BHQ-1 molecule. It has been suggested that the decrease of QDs PL occurred through a Forster resonance energy transfer (FRET) mechanism from the analysis of steady state photoluminescence intensity measurements as well as time resolved lifetime measurements of streptavidin-QDs and QDs(pep-BHQ-1)(n) conjugates. The sequence of intermediate peptide GPLG down arrow VRGK can act as a target material for matrix metalloproteinases-2 (MMP-2) produced by cancer cells at its Gly and Val region, shown by the down-headed arrow. Interestingly, here the reported self-assembled QDs-(pep-BHQ-1)(n) conjugates could detect the presence MMP-2 at a detection limit of 1 ng/mL with a clear luminescence recovery.
• X-ray diffraction line profile analysis of nanostructured nickel oxide: Shape factor and convolution of crystallite size and microstrain contributions

  K. Maniammal, G. Madhu, V. Biju

  Physica E: Low-dimensional Systems and Nanostructures 85 214 - 222 2017年01月
• Channeling Exciton Migration into Electron Transfer in Formamidinium Lead Bromide Perovskite Nanocrystal/Fullerene Composites

  Vijayakumar C. Nair, Chinnadurai Muthu, Andrey L. Rogach, Reiko Kohara, Vasudevanpillai Biju

  ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 56 5 1214 - 1218 2017年01月 [査読有り][通常論文]
   

  Hydrophobically capped nanocrystals of formamidinium lead bromide (FAPbBr(3)) perovskite (PNC) show bright and stable fluorescence in solution and thin-film states. When compared with isolated PNCs in a solution, closepacked PNCs in a thin film show extended fluorescence lifetime (ca. 4.2 mu s), which is due to hopping or migration of photogenerated excitons among PNCs. Both fluorescence quantum efficiency and lifetime decrease in a PNC thin film doped with fullerene (C-60), which is attributed to channeling of exciton migration into electron transfer to C-60. On the other hand, quenching of fluorescence intensity of a PNC solution is not accompanied by any change in fluorescence lifetime, indicating static electron transfer to C-60 adsorbed onto the hydrophobic surface of individual PNCs. Exciton migration among close-packed PNCs and electron transfer to C-60 places C-60-doped PNC thin films among cost-effective antenna systems for solar cells.
• In vivo ROS production and use of oxidative stress-derived biomarkers to detect the onset of diseases such as Alzheimer’s disease, Parkinson’s disease, and diabetes

  Aya Umeno, Vasudevanpillai Biju, Yasukazu Yoshida

  Free radical research 51 4 413 - 427 2017年 [査読有り][通常論文]
   

  Breakthroughs in biochemistry have furthered our understanding of the onset and progression of various diseases, and have advanced the development of new therapeutics. Oxidative stress and reactive oxygen species (ROS) are ubiquitous in biological systems. ROS can be formed nonenzymatically by chemical, photochemical and electron transfer reactions, or as the byproducts of endogenous enzymatic reactions, phagocytosis, and inflammation. Imbalances in ROS homeostasis, caused by impairments in antioxidant enzymes or non-enzymatic antioxidant networks, increase oxidative stress, leading to the deleterious oxidation and chemical modification of biomacromolecules such as lipids, DNA, and proteins. While many ROS are intracellular signaling messengers and most products of oxidative metabolisms are beneficial for normal cellular function, the elevation of ROS levels by light, hyperglycemia, peroxisomes, and certain enzymes causes oxidative stress-sensitive signaling, toxicity, oncogenesis, neurodegenerative diseases, and diabetes. Although the underlying mechanisms of these diseases are manifold, oxidative stress caused by ROS is a major contributing factor in their onset. This review summarizes the relationship between ROS and oxidative stress, with special reference to recent advancements in the detection of biomarkers related to oxidative stress. Further, we will introduce biomarkers for the early detection of neurodegenerative diseases and diabetes, with a focus on our recent work.
• Sensing of ozone based on its quenching effect on the photoluminescence of CdSe-based core-shell quantum dots

  Masanori Ando, Takuya Kamimura, Koichi Uegaki, Vasudevanpillai Biju, Yasushi Shigeri

  MICROCHIMICA ACTA 183 11 3019 - 3024 2016年11月 [査読有り][通常論文]
   

  Thin films of CdSe-based core-shell type quantum dots (CdSe/CdZnS, CdSe/ZnS and CdSeTe/ZnS) deposited on glass substrate were found to undergo a reversible change in photoluminescence (PL) on exposure to ozone in concentrations as low as 0.1 ppm in air. PL decreased rapidly on adding ozone and fully recovered after changing back to pure air. The PL of the CdSe/ZnS quantum dots (QDs) was not quenched by pure oxygen, nitrogen, argon, carbon dioxide, and air containing hydrogen. A comparison of various CdSe-based core-shell type QDs with different emission colors showed that green-emitting QDs with smaller size were more sensitive to ozone, while red-emitting QDs (of larger size) were more resistant to high concentrations of ozone. The response time of the sensor (for a 90 % signal change) was in the order of 10-20 min. The reversible, reproducible and selective response to ozone at room temperature under atmospheric pressure suggested that these QDs have a great potential in terms of fluorescent sensing of ozone.
• Latest impact factor

  Martin Vacha, Jong-Hyun Ahn, Vasudevan Pillai Biju, Tomoyasu Taniyama, Ikuyoshi Tomita, Shutao Wang, Jihui Yang

  NPG ASIA MATERIALS 8 2016年07月 [査読有り][通常論文]
  
• Intracellular accumulation of indium ions released from nanoparticles induces oxidative stress, proinflammatory response and DNA damage

  Yosuke Tabei, Akinari Sonoda, Yoshihiro Nakajima, Vasudevanpillai Biju, Yoji Makita, Yasukazu Yoshida, Masanori Horie

  JOURNAL OF BIOCHEMISTRY 159 2 225 - 237 2016年02月 [査読有り][通常論文]
   

  Due to the widespread use of indium tin oxide (ITO), it is important to investigate its effect on human health. In this study, we evaluated the cellular effects of ITO nanoparticles (NPs), indium chloride (InCl3) and tin chloride (SnCl3) using human lung epithelial A549 cells. Transmission electron microscopy and inductively coupled plasma mass spectrometry were employed to study cellular ITO NP uptake. Interestingly, greater uptake of ITO NPs was observed, as compared with soluble salts. ITO NP species released could be divided into two types: 'indium release ITO' or 'tin release ITO'. We incubated A549 cells with indium release ITO, tin release ITO, InCl3 or SnCl2 and investigated oxidative stress, proinflammatory response, cytotoxicity and DNA damage. We found that intracellular reactive oxygen species were increased in cells incubated with indium release ITO, but not tin release ITO, InCl3 or SnCl2. Messenger RNA and protein levels of the inflammatory marker, interleukin-8, also increased following exposure to indium release ITO. Furthermore, the alkaline comet assay revealed that intracellular accumulation of indium ions induced DNA damage. Our results demonstrate that the accumulation of ionic indium, but not ionic tin, from ITO NPs in the intracellular matrix has extensive cellular effects.
• Fluorescence detection of the pathogenic bacteria Vibrio harveyi in solution and animal cells using semiconductor quantum dots

  Esha Arshad, Abdulaziz Anas, Aparna Asok, C. Jasmin, Somnath S. Pai, I. S. Bright Singh, A. Mohandas, Vasudevanpillai Biju

  RSC ADVANCES 6 19 15686 - 15693 2016年 [査読有り][通常論文]
   

  Validation of microbial infection pathways in eukaryotic cells is challenging in the control of various infectious diseases. Semiconductor nanocrystals, also called quantum dots (QD), due to their exceptional brightness and photostability can be exploited in the long term monitoring of pathogens in host cells. However, the limited information about interactions of QDs and their bioconjugates with microorganisms confines the microbiological applications of QDs. Here we investigate the binding and toxicity of CdSe/ZnS QDs to the free-swimming marine pathogenic bacteria Vibrio harveyi using fluorescence microscopy, elastase assay, polyacrylamide gel electrophoresis (PAGE), and comet assay. The electrostatic binding of QDs to the cell surface has been found effective for the detection of the bacteria in aqueous solutions and bacteria-infected mammalian cells. The electrostatic binding is evaluated by the transient reversal of the cell surface charge contributed by macromolecules such as heparan sulfate proteoglycan (HSPG). Essentially, no fluorescence is detected for those bacteria treated with NiCl2 that reverses the cell surface charge. On the other hand, the efficiency of the cell surface to adsorb QDs remains intact even after treatment with elastase, which denatures the outer membrane proteins (Omps), suggesting HSPG-based binding of QD to cell surface and subsequently QDs are internalized. PAGE and comet assays show that the interactions of QDs with V. harveyi do not impart any cytotoxicity or genotoxicity. Further, we evaluate the integrity of adsorbed QDs for the detection of bacterial infection to mammalian cells by taking mouse fibroblast L929 as the model. Here, the stable fluorescence of QDs present in V. harveyi enables us for identifying the infected host cells. In short, the current study shows the potentials of for the detection of pathogens but without causing any toxic effects, which can be a promising method for not only the detection of the progression or regression of pathogenic infections but also phototherapy of microbial infections.
• Single-particle spectroscopy of I-III-VI semiconductor nanocrystals: spectral diffusion and suppression of blinking by two-color excitation

  Dharmendar Kumar Sharma, Shuzo Hirata, Lukasz Bujak, Vasudevanpillai Biju, Tatsuya Kameyama, Marino Kishi, Tsukasa Torimoto, Martin Vacha

  NANOSCALE 8 28 13687 - 13694 2016年 [査読有り][通常論文]
   

  Ternary I-III-VI semiconductor nanocrystals have been explored as non-toxic alternatives to II-VI semiconductors for optoelectronic and sensing applications, but large photoluminescence spectral width and moderate brightness restrict their practical use. Here, using single-particle photoluminescence spectroscopy on nanocrystals of (AgIn)(x)Zn2(1-x)S2 we show that the photoluminescence band is inhomogeneously broadened and that size distribution is the dominant factor in the broadening. The residual homogeneous linewidth of individual nanocrystals reaches up to 75% of the ensemble spectral width. Single nanocrystals undergo spectral diffusion which also contributes to the inhomogeneous band. Excitation with two lasers with energies above and below the bandgap reveals coexistence of two emitting donor states within one particle. Spectral diffusion in such particles is due to temporal activation and deactivation of one such state. Filling of a trap state with a lower-energy laser enables optical modulation of photoluminescence intermittency (blinking) and leads to an almost two-fold increase in brightness.
• Defect induced ferromagnetic interaction in nanostructured nickel oxide with core–shell magnetic structure: the role of Ni2+ and O2− vacancies

  G. Madhu, K. Maniammal, V. Biju

  Physical Chemistry Chemical Physics 18 17 12135 - 12148 2016年 

  O²⁻ vacancies act as donor impurities and mediate ferromagnetic interaction between spins associated with uncompensated and partially compensated Ni²⁺ vacancies.

• Fluorescence Quenching of CdSe/ZnS Quantum Dots by Using Black Hole Quencher Molecules Intermediated With Peptide for Biosensing Application.

  Sreenadh Sasidharan Pillai, Hiroshi Yukawa, Daisuke Onoshima, Vasudevanpillai Biju, Yoshinobu Baba

  Cell medicine 8 1-2 57 - 62 2015年12月17日 [査読有り][通常論文]
   

  Quantum dots (QDs) have recently been investigated as fluorescent probes for detecting a very small number of biomolecules and live cells; however, the establishment of molecular imaging technology with on-off control of QD fluorescence remains to be established. Here we have achieved the fluorescence off state of QDs with the conjugation of black hole quencher (BHQ) molecules intermediated with peptide by using streptavidin-QDs585 and biotin-pep-BHQ-1. The fluorescence of streptavidin-QDs585 was decreased by the addition of biotin-pep-BHQ-1 in a dose-dependent manner. It has been suggested that the decrease in QDs585 fluorescence occurred through a Förster resonance energy transfer (FRET) mechanism from the analysis of fluorescence intensity and lifetime of streptavidin-QDs585 and QDs585-pep-BHQ-1. QDs585 fluorescence could be quenched by more than 60% efficiency in this system. The sequence of intermediate peptide (pep) was GPLGVRGK, which can be cleaved by matrix metalloproteinases (MMPs) produced by cancer cells. QDs585-pep-BHQ-1 is thus expected to detect the MMP production by the recovery of QDs585 fluorescence as a new bioanalytical agent for molecular imaging.
• Fluctuating single sp(2) carbon clusters at single hotspots of silver nanoparticle dimers investigated by surface-enhanced resonance Raman scattering

  Tamitake Itoh, Yuko S. Yamamoto, Vasudevanpillai Biju, Hiroharu Tamaru, Shin-ichi Wakida

  AIP ADVANCES 5 12 2015年12月 [査読有り][通常論文]
   

  We evaluate spectral changes in surface enhanced resonance Raman scattering (SERRS) of near-single dye molecules in hotspots of single Ag nanoparticle (NP) dimers. During the laser excitation, surface enhance florescence (SEF) of dye disappeared and the number of SERRS lines decreased until finally ca. two lines remained around 1600 and 1350 cm(-1), those are evidence of G and D lines of single sp(2) carbon clusters. Analysis of the G and D line intensity ratios reveals the temporal fluctuation in the crystallite size of the clusters within several angstroms; whereas, broadening and splitting in the lines enable us for identifying directly the dynamics of various defects in the clusters. This analysis reveals that the detailed fluctuations of single sp(2) carbon clusters, which would be impossible to gain with other microscopic methods. (C) 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.
• Auger Ionization Beats Photo-Oxidation of Semiconductor Quantum Dots: Extended Stability of Single-Molecule Photoluminescence

  Shin-ichi Yamashita, Morihiko Hamada, Shunsuke Nakanishi, Hironobu Saito, Yoshio Nosaka, Shin-ichi Wakida, Vasudevanpillai Biju

  ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 54 13 3892 - 3896 2015年03月 [査読有り][通常論文]
   

  Despite the bright and tuneable photoluminescence (PL) of semiconductor quantum dots (QDs), the PL instability induced by Auger recombination and oxidation poses a major challenge in single-molecule applications of QDs. The incomplete information about Auger recombination and oxidation is an obstacle in the resolution of this challenge. Here, we report for the first time that Auger-ionized QDs beat self-sensitized oxidation and the non-digitized PL intensity loss. Although high-intensity photoactivation insistently induces PL blinking, the transient escape of QDs into the ultrafast Auger recombination cycle prevents generation of singlet oxygen (O-1(2)) and preserves the PL intensity. By the detection of the NIR phosphorescence of O-1(2) and evaluation of the photostability of single QDs in aerobic, anaerobic, and O-1(2) scavenger-enriched environments, we disclose relations of Auger ionization and O-1(2)-mediated oxidation to the PL stability of single QDs, which will be useful during the formulation of QD-based single-molecule imaging tools and single-photon devices.
• In vitro evaluation of the cellular effect of indium tin oxide nanoparticles using the human lung adenocarcinoma A549 cells

  Yosuke Tabei, Akinari Sonoda, Yoshihiro Nakajima, Vasudevanpillai Biju, Yoji Makita, Yasukazu Yoshida, Masanori Horie

  METALLOMICS 7 5 816 - 827 2015年 [査読有り][通常論文]
   

  Indium tin oxide (ITO) is widely used in liquid crystal displays (LCDs) or plasma and mobile phone displays. Elevated production and usage of ITO in such displays have led to increased concerns over the safety of industrial workers exposed to particulate aerosols produced during cutting, grinding and polishing of these materials. However, the cellular effects of ITO nanoparticles (NPs) are still unclear, although it has been reported that micro-scale ITO particles induce cytotoxicity. The aim of this study was to examine the potential of ITO NPs to induce cytotoxicity, oxidative stress, and DNA damage using human lung adenocarcinoma A549 cells. Here, stable dispersions of a medium containing ITO NPs were obtained using pre-adsorption and centrifugal fractionation methods, and the A549 cells were incubated in this medium. The ITO NPs showed low cytotoxic effects as shown by the WST-1 and LDH assays. Transmission electron microscopy observations showed the cellular uptake of ITO NPs. The ITO NPs increased the intracellular level of reactive oxygen species and the expression of the heme oxygenase 1 gene. Further, the results of alkaline comet assays showed that ITO NPs induced DNA damage. Thus, these results suggest that ITO NPs possess a genotoxic potential on human lung adenocarcinoma A549 cells.
• Nanoparticles speckled by ready-to-conjugate lanthanide complexes for multimodal imaging

  Vasudevanpillai Biju, Morihiko Hamada, Kenji Ono, Sakiko Sugino, Takashi Ohnishi, Edakkattuparambil Sidharth Shibu, Shohei Yamamura, Makoto Sawada, Shunsuke Nakanishi, Yasushi Shigeri, Shin-ichi Wakida

  NANOSCALE 7 36 14829 - 14837 2015年 [査読有り][通常論文]
   

  Multimodal and multifunctional contrast agents receive enormous attention in the biomedical imaging field. Such contrast agents are routinely prepared by the incorporation of organic molecules and inorganic nanoparticles (NPs) into host materials such as gold NPs, silica NPs, polymer NPs, and liposomes. Despite their non-cytotoxic nature, the large size of these NPs limits the in vivo distribution and clearance and inflames complex pharmacokinetics, which hinder the regulatory approval for clinical applications. Herein, we report a unique method that combines magnetic resonance imaging (MRI) and fluorescence imaging modalities together in nanoscale entities by the simple, direct and stable conjugation of novel biotinylated coordination complexes of gadolinium(III) to CdSe/ZnS quantum dots (QD) and terbium(III) to super paramagnetic iron oxide NPs (SPION) but without any host material. Subsequently, we evaluate the potentials of such lanthanide-speckled fluorescent-magnetic NPs for bioimaging at single-molecule, cell and in vivo levels. The simple preparation and small size make such fluorescent-magnetic NPs promising contrast agents for biomedical imaging.
• Single-molecular surface-enhanced resonance Raman scattering as a quantitative probe of local electromagnetic field: The case of strong coupling between plasmonic and excitonic resonance

  Tamitake Itoh, Yuko S. Yamamoto, Hiroharu Tamaru, Vasudevanpillai Biju, Shin-ichi Wakida, Yukihiro Ozaki

  PHYSICAL REVIEW B 89 19 2014年05月 [査読有り][通常論文]
   

  We investigate electromagnetic coupling between plasmonic and molecular electronic resonances using single-molecular surface-enhanced resonance Raman scattering (SERRS) from single silver nanoparticle dimers. When dimers exhibit SERRS activity, their elastic light scattering spectra show two lines, which are temporally closing toward each other. The higher energy line eventually disappears at the time of SERRS quenching. A coupled-oscillator model composed of plasmonic and molecular electronic resonances consistently reproduces the above interesting results by decreasing coupling energy, indicating that SERRS can be a quantitative probe for strong coupling between the two resonances.
• Photoluminescence of CdSe and CdSe/ZnS quantum dots: Modifications for making the invisible visible at ensemble and single-molecule levels

  Edakkattuparambil S. Shibu, Morihiko Hamada, Shunsuke Nakanishi, Shin-ichi Wakida, Vasudevanpillai Biju

  COORDINATION CHEMISTRY REVIEWS 263 2 - 12 2014年03月 [査読有り][通常論文]
   

  This thematic article is written with an intention to provide an overview of our recent research on the modulation of quantum dots photoluminescence and the applications of quantum dots to bioimaging. In particular, we summarize the physiochemical factors that affect the photoluminescence of CdSe or CdSe/ZnS quantum dots at ensemble and single-molecule levels, blinking and blinking suppression of quantum dots, bioconjugation of quantum dots, applications of bioconjugated quantum dots for analyzing some selected biophysical processes at single-molecule levels, and intracellular delivery of quantum dot bioconjugates. These research subjects are correlated with the state of the art accomplishments in the quantum dot field. (C) 2013 Elsevier B.V. All rights reserved.
• In Situ Photochemical Surface Passivation of CdSe/ZnS Quantum Dots for Quantitative Light Emission and Enhanced Photocurrent Response in Solar Cells

  Morihiko Hamada, Norifumi Takenokoshi, Keiji Matozaki, Qi Feng, Norio Murase, Shin-ichi Wakida, Shunsuke Nakanishi, Vasudevanpillai Biju

  JOURNAL OF PHYSICAL CHEMISTRY C 118 4 2178 - 2186 2014年01月 [査読有り][通常論文]
   

  Suppression of energy-wasting nonradiative carrier relaxation in photo-activated semiconductor quantum dots (QDs) is an essential requirement for applications such as QD-sensitized solar cell (QDSSC). Here we report that in situ surface passivation of CdSe/ZnS QDs using dithiothreitol (DTT) results in the 4-fold enhancement of photoluminescence (PL) quantum efficiency of QDs. By the analyses of PL intensities and blinking statistics of single QDs, the PL enhancement is assigned to a combination of processes such as unexpected appearance of bright QDs, gradual increase in the PL intensity of QDs, and substantial suppression of blinking. These processes not only suggest the suppression of nonradiative carrier recombination in QDs passivated with DTT molecules but also enable us to classify the nonradiative carrier recombination centers in QDs into low-density defects in which the rates of nonradiative recombination largely exceed the rates of radiative relaxation and high-density defects in which the rates of nonradiative carrier recombination are comparable to the rates of radiative relaxations. In the former case, passivation of the defects by the spontaneous addition of one or a few DTT molecules to QDs with PL intensity below the detection limit results in the formation of highly luminescent QD-(DTT)(n) adducts. In the latter case, highly luminescent QD-(DTT)(n) adducts are formed from already luminescent QDs by the relatively slow addition of DTT molecules. These two types of surface passivation reactions are governed by both chemical and photochemical processes. Overall, the passivation of defects in QD by DTT results in the suppression of energy-wasting nonradiative relaxations, which enables us to drive ca. 33% excess photocurrent in a photoelectrochemical cell constructed using QD-(DTT)(n) as the sensitizer.
• SERS microscopic imaging as novel tool for assessing viability and enumerating yeast cells at various stages of cell cycle in lag, log, exponential and stationary phases of growth in culture

  Manikantan Syamala Kiran, Tamitake Itoh, Hiroko Abe, Yasuko Fujita, Kazuya Tomimoto, Vasudevanpillai Biju, Sajani Kavitha, Arumugham Ganamani, Mitsuru Ishikawa

  JOURNAL OF EXPERIMENTAL NANOSCIENCE 9 10 1003 - 1014 2014年 [査読有り][通常論文]
   

  Surface enhanced Raman scattering (SERS) microscopic imaging was employed to enumerate the yeast cells in culture. We found this imaging method as an efficient tool for easily differentiating and quantitatively enumerating yeast cell at different stages of cell-division cycle (G1, S, G2 and M phase) at various stages of growth phases namely lag, log, exponential and stationary phases in culture. Apart from enumerating the cells at different stages of cell cycle under lag, log, exponential and stationary phases, it was possible using SERS microscopy to differentiate the live cells from dead ones. The dead cells were SERS inactive and gave enhanced autofluorescence compared with the live cells, which were SERS active. The results from the present investigation suggest that SERS microscopic imaging, using silver nanoparticles (AgNPs) as a sensitive tool to enumerate the yeast cells in culture.
• Chemical modifications and bioconjugate reactions of nanomaterials for sensing, imaging, drug delivery and therapy

  Vasudevanpillai Biju

  CHEMICAL SOCIETY REVIEWS 43 3 744 - 764 2014年 [査読有り][通常論文]
   

  As prepared nanomaterials of metals, semiconductors, polymers and carbon often need surface modifications such as ligand exchange, and chemical and bioconjugate reactions for various biosensor, bioanalytical, bioimaging, drug delivery and therapeutic applications. Such surface modifications help us to control the physico-chemical, toxicological and pharmacological properties of nanomaterials. Furthermore, introduction of various reactive functional groups on the surface of nanomaterials allows us to conjugate a spectrum of contrast agents, antibodies, peptides, ligands, drugs and genes, and construct multifunctional and hybrid nanomaterials for the targeted imaging and treatment of cancers. This tutorial review is intended to provide an introduction to newcomers about how chemical and bioconjugate reactions transform the surface of nanomaterials such as silica nanoparticles, gold nanoparticles, gold quantum clusters, semiconductor quantum dots, carbon nanotubes, fullerene and graphene, and accordingly formulate them for applications such as biosensing, bioimaging, drug and gene delivery, chemotherapy, photodynamic therapy and photothermal therapy. Nonetheless, controversial reports and our growing concerns about toxicity and pharmacokinetics of nanomaterials suggest the need for not only rigorous in vivo experiments in animal models but also novel nanomaterials for practical applications in the clinical settings. Further reading of original and review articles cited herein is necessary to buildup in-depth knowledge about the chemistry, bioconjugate chemistry and biological applications of individual nanomaterials.
• Photouncaging Nanoparticles for MRI and Fluorescence Imaging in Vitro and in Vivo

  Edakkattuparambil S. Shibu, Kenji Ono, Sakiko Sugino, Ayami Nishioka, Akikazu Yasuda, Yasushi Shigeri, Shin-ichi Wakida, Makoto Sawada, Vasudevanpillai Biju

  ACS NANO 7 11 9851 - 9859 2013年11月 [査読有り][通常論文]
   

  Multimodal and multifunctional nanomaterials are promising candidates for bioimaging and therapeutic applications in the nanomedicine settings. Here we report the preparation of photouncaging nanoparticles with fluorescence and magnetic modalities and evaluation of their potentials for in vitro and in vivo bioimaging. Photoactivation of such bimodal nanoparticles prepared using photouncaging ligands, CdSe/ZnS quantum dots, and super paramagnetic iron oxide nanoparticles results in the systematic uncaging of the particles, which is correlated with continuous changes in the absorption, mass and NMR spectra of the ligands. Fluorescence and magnetic components of the bimodal nanoparticles are characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and elemental analyses using energy dispersive X-ray (MX) spectroscopy and X-ray photoelectron spectroscopy (XPS). Bioconjugation of the nanoparticles with peptide hormones renders them with biocompatibility and efficient intracellular transport as seen in the fluorescence and MRI images of mouse melanoma cells (B16) or human lung epithelial adenocarcinoma cells (H1650). Biocompatibility of the nanoparticles is evaluated using MU cytotoxicity assays, which show cell viability over 90%. Further, we combine MRI and NIR fluorescence imaging in C578116 (136) mice subcutaneously or intravenously injected with the photouncaging nanoparticles and follow the in vivo fate of the nanoparticles. Interestingly, the intravenously injected nanoparticles initially accumulate in the liver within 30 min post injection and subsequently clear by the renal excretion within 48 h as seen in the time-dependent MRI and fluorescence images of the liver, urinary bladder, and urine samples. Photouncaging ligands such as the ones reported in this article are promising candidates for not only the site-specific delivery of nanomaterials-based contrast agents and drugs but also the systematic uncaging and renal clearance of nanomaterials after the desired in vivo application.
• Singlet-Oxygen-Sensitizing Near-Infrared-Fluorescent Multimodal Nanoparticles

  Edakkattuparambil Sidharth Shibu, Sakiko Sugino, Kenji Ono, Hironobu Saito, Ayama Nishioka, Shohei Yamamura, Makoto Sawada, Yoshio Nosaka, Vasudevanpillai Biju

  ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 52 40 10559 - 10563 2013年09月 [査読有り][通常論文]
  
• Single Quantum Dot Tracking Reveals that an Individual Multivalent HIV-1 Tat Protein Transduction Domain Can Activate Machinery for Lateral Transport and Endocytosis

  Yasuhiro Suzuki, Chandra Nath Roy, Warunya Promjunyakul, Hiroyasu Hatakeyama, Kohsuke Gonda, Junji Imamura, Biju Vasudevanpillai, Noriaki Ohuchi, Makoto Kanzaki, Hideo Higuchi, Mitsuo Kaku

  MOLECULAR AND CELLULAR BIOLOGY 33 15 3036 - 3049 2013年08月 [査読有り][通常論文]
   

  The mechanisms underlying the cellular entry of the HIV-1 Tat protein transduction domain (TatP) and the molecular information necessary to improve the transduction efficiency of TatP remain unclear due to the technical limitations for direct visualization of TatP's behavior in cells. Using confocal microscopy, total internal reflection fluorescence microscopy, and four-dimensional microscopy, we developed a single-molecule tracking assay for TatP labeled with quantum dots (QDs) to examine the kinetics of TatP initially and immediately before, at the beginning of, and immediately after entry into living cells. We report that even when the number of multivalent TatP (mTatP)-QDs bound to a cell was low, each single mTatP-QD first locally induced the cell's lateral transport machinery to move the mTatP-QD toward the center of the cell body upon cross-linking of heparan sulfate proteoglycans. The centripetal and lateral movements were linked to the integrity and flow of actomyosin and microtubules. Individual mTatP underwent lipid raft-mediated temporal confinement, followed by complete immobilization, which ultimately led to endocytotic internalization. However, bivalent TatP did not sufficiently promote either cell surface movement or internalization. Together, these findings provide clues regarding the mechanisms of TatP cell entry and indicate that increasing the valence of TatP on nanoparticles allows them to behave as cargo delivery nanomachines.
• Effects of Interactions with Cyclic Solvent Molecules on Optical Dephasing of CdSe/ZnS Colloidal Quantum Dots Detected by Femtosecond Four-Wave Mixing Spectroscopy

  Yusuke Hirosawa, Hiroyoshi Kouzai, Naoya Yamazaki, Hayato Miyagawa, Noriaki Tsurumachi, Shun Koshiba, Shunsuke Nakanishi, VasudevanPillai Biju, Mituru Ishikawa

  JAPANESE JOURNAL OF APPLIED PHYSICS 52 7 2013年07月 [査読有り][通常論文]
   

  We have studied the effects of interactions with cyclic solvent molecules on the optical dephasing of CdSe/ZnS colloidal quantum dots (QDs) by femtosecond four-wave mixing spectroscopy. We have found that the interactions with the cyclic solvents without p-bonds result in unexpectedly long dephasing times of QDs even at room temperature, while the interactions with the cyclic solvents including p-bonds make the optical dephasing of QDs extremely fast with a dephasing time of less than our time resolution. (C) 2013 The Japan Society of Applied Physics
• Excitation laser energy dependence of surface-enhanced fluorescence showing plasmon-induced ultrafast electronic dynamics in dye molecules

  Tamitake Itoh, Yuko S. Yamamoto, Hiroharu Tamaru, Vasudevanpillai Biju, Norio Murase, Yukihiro Ozaki

  PHYSICAL REVIEW B 87 23 2013年06月 [査読有り][通常論文]
   

  We find unique properties accompanying surface-enhanced fluorescence (SEF) from dye molecules adsorbed on Ag nanoparticle aggregates, which generate surface-enhanced Raman scattering. The properties are observed in excitation laser energy dependence of SEF after excluding plasmonic spectral modulation in SEF. The unique properties are large blue shifts of fluorescence spectra, deviation of ratios between anti-Stokes SEF intensity and Stokes from those of normal fluorescence, super-broadening of Stokes spectra, and returning to original fluorescence by lower energy excitation. We elucidate that these properties are induced by electromagnetic enhancement of radiative decay rates exceeding the vibrational relaxation rates within an electronic excited state, which suggests that molecular electronic dynamics in strong plasmonic fields can be largely deviated from that in free space.
• Nanomaterials formulations for photothermal and photodynamic therapy of cancer

  Edakkattuparambil Sidharth Shibu, Morihiko Hamada, Norio Murase, Vasudevanpillai Biju

  JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY C-PHOTOCHEMISTRY REVIEWS 15 53 - 72 2013年06月 [査読有り][通常論文]
   

  Nanomaterials with well-defined size, shape, composition, and surface functionalities offer multimodal and multifunctional platforms for various bioanalytical, bioimaging, and therapeutic applications. In this review, we focus on the different theranostic formulations of nanomaterials based on gold, silver, silica, semiconductor quantum dots, upconversion lanthanides, oxide magnets, polymers, liposomes, carbon nanotubes, graphene and carbon nanohorns, and their applications in photothermal and photodynamic therapy of cancer. (C) 2012 Elsevier B.V. All rights reserved.
• Dynamic Interactions of CdSe/Zns Quantum Dots with Cyclic Solvents Probed by Femtosecond Four-Wave Mixing

  Y. Hirosawa, H. Kouzai, H. Miyagawa, N. Tsurumachi, S. Koshiba, S. Nakanishi, V. Biju, M. Ishikawa

  XVIIITH INTERNATIONAL CONFERENCE ON ULTRAFAST PHENOMENA 41 2013年 [査読有り][通常論文]
   

  We studied dynamic interactions between CdSe/ZnS quantum dots (QDs) and cyclic solvents probed by femtosecond four-wave mixing. We found that the dynamic interactions of QDs strongly depend on the existence of p-bonds in solvent molecules.
• Impairments of cells and genomic DNA by environmentally transformed engineered nanomaterials

  Philip Jones, Sakiko Sugino, Shohei Yamamura, Fred Lacy, Vasudevanpillai Biju

  NANOSCALE 5 20 9511 - 9516 2013年 [査読有り][通常論文]
   

  Enormous increase in the production of nanomaterials and their growing applications in the device technology, biotechnology and biomedical areas suggest the need for developing models for predicting the environmental health and safety (EHS) risks posed by such nanomaterials. We hypothesize that CdSe quantum dots (QDs) and ZnO nanoparticles (NPs) encompassed in liposomes or not and transformed by simulated solar UV light can be model systems for studying the environmental toxicity of engineered nanomaterials. In this study, human lung epithelial adenocarcinoma cells (H1650) are exposed to photoirradiated CdSe QDs or ZnO nanopowder included or not in liposomes. The release of cadmium and zinc ions from the nanomaterials exposed to solar simulated UV radiation is detected and quantified by measuring the steady-state and time resolved fluorescence of the metal ion sensor tetracarboxyphenylporphyrin (TCPP) or the commercial Measure iT Pd/Cd sensor. Viability of cells treated with nanomaterials exposed to solar simulated UV radiation for different durations is measured by MTT assay. Enhanced etching of the nanoparticles exposed to solar simulated UV radiation results in the release of toxic levels of heavy metal ions, which considerably lower the viability of H1650 cells is due to the deactivation of DNA repair enzymes as evidenced by the pinching off of nuclear DNA in comet assays and DNA samples in electrophoresis. Results from this study highlight the need to obtain not only quantitative information about the environmental risks posed by engineered nanomaterials but also environment friendly nanomaterials for practical applications.
• Inhibition Assay of Yeast Cell Walls by Plasmon Resonance Rayleigh Scattering and Surface-Enhanced Raman Scattering Imaging

  Kiran Manikantan Syamala, Hiroko Abe, Yasuko Fujita, Kazuya Tomimoto, Vasudevanpillai Biju, Mitsuru Ishikawa, Yukihiro Ozaki, Tamitake Itoh

  LANGMUIR 28 24 8952 - 8958 2012年06月 [査読有り][通常論文]
   

  We report on plasmon resonance Rayleigh scattering (PRRS) and surface enhanced Raman scattering (SERS) imaging for inhibition assay of yeast cell walls. This assay reveals that the proteins having alkali sensitive linkage bound to beta 1,3 glucan frameworks in cell walls are involved in SERS activity. The result is further confirmed by comparison of genetically modified cells and wild type cells. Finally, we find that PARS and SERS spots do not appear on cell walls when daughter cells are enough smaller than parent ones, but appear when size of daughter cells are comparable to parent cells. This finding indicates the relationship between expression of the proteins that generate SERS spots and cell division. These results demonstrate that PRRS and SERS imaging can be a convenient and sensitive method for analysis of cell walls.
• FRET from Quantum Dots to Photodecompose Undesired Acceptors and Report the Condensation and Decondensation of Plasmid DNA

  Vasudevanpillai Biju, Abdulaziz Anas, Hidetaka Akita, Edakkattuparambil Sidharthan Shibu, Tamitake Itoh, Hideyoshi Harashima, Mitsuru Ishikawa

  ACS NANO 6 5 3776 - 3788 2012年05月 [査読有り][通常論文]
   

  Protection of genes against enzymatic degradation and overcoming of cellular barriers are critical for efficient gene delivery. The effectiveness of gene delivery by nonviral vectors depends mostly on the extent of DNA packaging or condensation. We show that Forster resonance energy transfer (FRET)-mediated photodecomposition of undesired acceptors In doubly labeled plasmid DNA (pDNA) and FRET recovery after acceptor photodecomposition (FRET-RAP) are effective methods for the detection of DNA condensation and decondensation. Our hypothesis is that undesired acceptors within the Forster distance of highly-photostable donors in precondensed DNA can be selectively photodecomposed by FRET. We Investigate this hypothesis by the random labeling of pcDNA3.1-GL3 and pUC18DNA with quantum dots (QDs) as the energy donor and AlexaFluor594 or Cy5 as the acceptor. At first, the random labeling generates efficient FRET, also called intrinsic FRET, in precondensed DNA, which prevents us from decoding any changes in the FRET efficiency during DNA condensation. Next, we suppressed the intrinsic FRET by the FRET-mediated photodecomposition of acceptors within the Forster distance of QDs. Conversely, many acceptors kept intact beyond the Forster distance provide us with high FRET efficiency during the condensation of pDNA using protamine. Further, the FRET efficiency is significantly decreased during the decondensation of DNA using heparan sulfate and glutathione. The random labeling of DNA using excess acceptors around photostable donors followed by the FRET-mediated photodecomposition of undesired acceptors can be a promising method for not only the sensitive detection of DNA condensation by FRET but also the customization of biomolecular sensors.
• Photofabrication of Fullerene-Shelled Quantum Dots Supramolecular Nanoparticles for Solar Energy Harvesting

  Edakkattuparambil Sidharth Shibu, Akinari Sonoda, Zhuoqiz Tao, Qi Feng, Akihiro Furube, Sadahiro Masuo, Li Wang, Naoto Tamai, Mitsuru Ishikawa, Vasudevanpillai Biju

  ACS NANO 6 2 1601 - 1608 2012年02月 [査読有り][通常論文]
   

  Quantum dots-based electron donor-acceptor systems play a rising role in the design of renewable and carbon-free energy harvesting technologies. In this article, we discuss the photofabrication of fullerene-shelled quantum dots supramolecular nanoparticles, in which the fullerene shell acts as not only a well-defined electron acceptor but also a robust protecting layer against the photocorrosion of the quantum dot core. We evaluate the ensemble and single-molecule electron transfer from the core to the shell in the nanoparticles and the photocurrent response of a photoelectrochiemical cell constructed using the nanopanicles. The supramolecular nanoparticle has been prepared by the covalent tethering of a fullerene-thiol monolayer to the quantum dot followed by the photochemical reactions of free fullerene-thiol to the tethered monolayer. The nanoparticles are characterized using scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. Correlated single-photon emission and the two-state ON-OFF photoluminescence show that single quantum dots are included In the supramolecular nanoparticles. The fullerene-shells suppress the blinking of single quantum dots by acting as well-defined electron traps, without allowing the transfer of Auger electrons to unknown traps. Electron transfer from the quantum dot-core to the fullerene-shell is apparent from the short ON and OFF durations in the photoluminescence intensity trajectories of single quantum dots, quenching of the photoluminescence intensity and lifetime of quantum dots at the ensemble level, and the characteristic transient absorption band of the anion radical of fullerene. We next construct a photoelectrochemical cell using the supramolecular nanoparticles, and the transferred electron is externally driven in the cell to generate similar to 400 mu A/crn(2) photocurrent. Electron transfer from the highly stable quantum dots to the protecting fullerene-shells places the supramolecular nanoparticles among the most promising antenna systems for the construction of cost-effective and stable next generation solar energy harvesting systems.
• Quantitative evaluation of blinking in surface enhanced resonance Raman scattering and fluorescence by electromagnetic mechanism

  Tamitake Itoh, Mitsuhiro Iga, Hiroharu Tamaru, Ken-ichi Yoshida, Vasudevanpillai Biju, Mitsuru Ishikawa

  JOURNAL OF CHEMICAL PHYSICS 136 2 2012年01月 [査読有り][通常論文]
   

  We analyze blinking in surface enhanced resonance Raman scattering (SERRS) and surface enhanced fluorescence (SEF) of rhodamine 6G molecules as intensity and spectral instability by electromagnetic (EM) mechanism. We find that irradiation of intense NIR laser pulses induces blinking in SERRS and SEF. Thanks to the finding, we systematically analyze SERRS and SEF from stable to unstable using single Ag nanoparticle (NP) dimers. The analysis reveals two physical insights into blinking as follows. (1) The intensity instability is inversely proportional to the enhancement factors of decay rate of molecules. The estimation using the proportionality suggests that separation of the molecules from Ag NP surfaces is several angstroms. (2) The spectral instability is induced by blueshifts in EM enhancement factors, which have spectral shapes similar to the plasmon resonance. This analysis provides us with a quantitative picture for intensity and spectral instability in SERRS and SEF within the framework of EM mechanism. (C) 2012 American Institute of Physics. [doi:10.1063/1.3675567]
• Quantitative analysis of condensation/decondensation status of pDNA in the nuclear sub-domains by QD-FRET

  Sharif M. Shaheen, Hidetaka Akita, Atsushi Yamashita, Ryo Katoono, Nobuhiko Yui, Vasudevanpillai Biju, Mitsuru Ishikawa, Hideyoshi Harashima

  NUCLEIC ACIDS RESEARCH 39 7 E48 - U108 2011年04月 [査読有り][通常論文]
   

  Recent studies indicate that controlling the nuclear decondensation and intra-nuclear localization of plasmid DNA (pDNA) would result in an increased transfection efficiency. In the present study, we established a technology for imaging the nuclear condensation/decondensation status of pDNA in nuclear subdomains using fluorescence resonance energy transfer (FRET) between quantum dot (QD)-labeled pDNA as donor, and rhodamine-labeled polycations as acceptor. The FRET-occurring pDNA/polycation particle was encapsulated in a nuclear delivery system; a tetra-lamellar multifunctional envelope-type nano device (T-MEND), designed to overcome the endosomal membrane and nuclear membrane via step-wise fusion. Nuclear subdomains (i.e. heterochromatin and euchromatin) were distinguished by Hoechst33342 staining. Thereafter, Z-series of confocal images were captured by confocal laser scanning microscopy. pDNA in condensation/decondensation status in heterochromatin or euchromatin were quantified based on the pixel area of the signals derived from the QD and rhodamine. The results obtained indicate that modulation of the supra-molecular structure of polyrotaxane (DMAE-ss-PRX), a condenser that is cleaved in a reductive environment, conferred euchromatin-preferred decondensation. This represents the first demonstration of the successful control of condensation/decondensation in specific nuclear sub-domain via the use of an artificial DNA condenser.
• Experimental demonstration of the electromagnetic mechanism underlying surface enhanced Raman scattering using single nanoparticle spectroscopy

  Tamitake Itoh, Ken-ichi Yoshida, Hiroharu Tamaru, Vasudevanpillai Biju, Mitsuru Ishikawa

  JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY 219 2-3 167 - 179 2011年04月 [査読有り][通常論文]
   

  Nanostructures and nanoparticles of Ag and Au offer large enhancements of optical responses such as optical absorption, Rayleigh and Raman scatterings and their nonlinear counterparts to adsorbed molecules. Such enhancements originate from the strong plasma (plasmon) resonance of Ag and Au and have been widely applied for the sensitive detection of various organic and biomolecules under the terminology of surface enhanced spectroscopy, the most common example being surface enhanced Raman scattering (SERS). Although SERS has turned out to be one of the most sensitive analytical techniques, fundamental issues such as lack of conclusive experimental evidence for validating the mechanism underlying SERS and difficulty to establish potential applications of SERS in daily life limit its recognition. Single nanoparticle spectroscopy due to its ability to correlate enhanced Raman scattering with other optical properties of metal nanoparticles is a powerful method for clarifying the mechanism underlying SERS. In this article, we review our recent advances in the experimental evaluation of SERS mechanism. In particular, using single nanoparticle spectroscopy, we attempted to quantitatively evaluate the enhancement mechanism underlying SERS at the onset of electromagnetic (EM) theory. Also, we briefly comment on the advantages of SERS over fluorescence spectroscopy for label-free detection of biomolecules by taking examples from our own investigations and recent reports by others. (C) 2011 Elsevier B.V. All rights reserved.
• Quantitative analysis of condensation/decondensation status of pDNA in the nuclear sub-domains by QD-FRET.

  Sharif M Shaheen, Hidetaka Akita, Atsushi Yamashita, Ryo Katoono, Nobuhiko Yui, Vasudevanpillai Biju, Mitsuru Ishikawa, Hideyoshi Harashima

  Nucleic Acids Res. 39 7 e48 - e48 2011年04月 [査読有り][通常論文]
   

  Recent studies indicate that controlling the nuclear decondensation and intra-nuclear localization of plasmid DNA (pDNA) would result in an increased transfection efficiency. In the present study, we established a technology for imaging the nuclear condensation/decondensation status of pDNA in nuclear subdomains using fluorescence resonance energy transfer (FRET) between quantum dot (QD)-labeled pDNA as donor, and rhodamine-labeled polycations as acceptor. The FRET-occurring pDNA/polycation particle was encapsulated in a nuclear delivery system; a tetra-lamellar multifunctional envelope-type nano device (T-MEND), designed to overcome the endosomal membrane and nuclear membrane via step-wise fusion. Nuclear subdomains (i.e. heterochromatin and euchromatin) were distinguished by Hoechst33342 staining. Thereafter, Z-series of confocal images were captured by confocal laser scanning microscopy. pDNA in condensation/decondensation status in heterochromatin or euchromatin were quantified based on the pixel area of the signals derived from the QD and rhodamine. The results obtained indicate that modulation of the supra-molecular structure of polyrotaxane (DMAE-ss-PRX), a condenser that is
• Bioconjugated quantum dots for cancer research: Present status, prospects and remaining issues (vol 28, pg 199, 2010)

  Vasudevanpillai Biju, Sathish Mundayoor, Ramakrishnapillai V. Omkumar, Abdulaziz Anas, Mitsuru Ishikawa

  BIOTECHNOLOGY ADVANCES 29 2 259 - 260 2011年03月 [査読有り][通常論文]
  
• Quantitative evaluation of electromagnetic enhancement in surface-enhanced resonance Raman scattering from plasmonic properties and morphologies of individual Ag nanostructures (vol 81, 115406, 2010)

  Ken-ichi Yoshida, Tamitake Itoh, Hiroharu Tamaru, Vasudevanpillai Biju, Mitsuru Ishikawa, Yukihiro Ozaki

  PHYSICAL REVIEW B 83 11 2011年03月 [査読有り][通常論文]
  
• Luminescent Quantum Dots, Making Invisibles Visible in Bioimaging

  Mitsuru Ishikawa, Vasudevanpillai Biju

  NANOPARTICLES IN TRANSLATIONAL SCIENCE AND MEDICINE 104 53 - 99 2011年 [査読有り][通常論文]
   

  Semiconductor quantum dots (QDs), their size-dependent tunable absorption and emission in the visible and near-infrared regions, narrow emission and broad absorption bands, large one- and multiphoton absorption cross sections, brightness, and photostability make them powerful light sources in the nano-scale region that will help to advance biotechnologies. This chapter overviews the present status and prospects of QDs by focusing on bioconjugation of QDs, and applications of bioconjugated QDs to surface-cell as well as inside-cell labeling for imaging and photodynamic therapy (PDT). In particular, it highlights the synthesis of biocompatible QDs, surface modification of QDs, conjugation of QDs with a variety of ligands and antibodies, potential targets of bioconjugated QDs in cells, nonspecific and specific surface-cell labeling, nonspecific and specific delivery of QDs in cells, and PDT based on QDs. Such information will be helpful for both applications of QDs for bioimaging and extension of QD technologies to other nanoparticles.
• Single-molecule photochemical reactions of Auger-ionized quantum dots.

  Hamada M, Shibu ES, Itoh T, Kiran MS, Nakanishi S, Ishikawa M, Biju V

  Nano reviews 2 2011年 [査読有り][通常論文]
   

  Photoinduced electron transfer in donor-acceptor systems composed of quantum dots (QDs) and electron donors or acceptors is a subject of considerable recent research interest due to the potential applications of such systems in both solar energy harvesting and degradation of organic pollutants. Herein, we employed single-molecule imaging and spectroscopy techniques for the detection of photochemical reactions between 1,4-diaminobutane (DAB) and CdSe/ZnS single QDs. We investigated the reactions by analyzing photoluminescence (PL) intensity and lifetime of QDs at ensemble and single-molecule levels. While DAB was applied to single QDs tethered on a cover slip or QDs dispersed in a solution, PL intensity of QD continuously decreased with a concomitant increase in the PL lifetime. Interestingly, these changes in the PL properties of QD were predominant under high-intensity photoactivation. We hypothesize that the above changes in the PL properties surface due to the transfer of an electron from DAB to Auger-ionized QD followed by elimination of a proton from DAB and the formation of a QD-DAB adduct. Thus, a continuous decrease in the PL intensity of QDs under high-intensity photoactivation is attributed to continuous photochemical reactions of DAB with single QDs and the formation of QD-(DAB)(n) adducts. We believe that detection and analysis of such photochemical reactions of single QDs with amines will be of considerable broad interest due to the significant impact of photoinduced electron transfer reactions in energy management and environmental remediation.
• Spectral variations in background light emission of surface-enhanced resonance hyper Raman scattering coupled with plasma resonance of individual silver nanoaggregates (vol 133, 124704, 2010)

  Tamitake Itoh, Hiroyuki Yoshikawa, Ken-ichi Yoshida, Vasudevanpillai Biju, Mitsuru Ishikawa

  JOURNAL OF CHEMICAL PHYSICS 133 14 2010年10月 [査読有り][通常論文]
  
• Spectral variations in background light emission of surface-enhanced resonance hyper Raman scattering coupled with plasma resonance of individual silver nanoaggregates

  Tamitake Itoh, Hiroyuki Yoshikawa, Ken-ichi Yoshida, Vasudevanpillai Biju, Mitsuru Ishikawa

  JOURNAL OF CHEMICAL PHYSICS 133 12 2010年09月 [査読有り][通常論文]
   

  We demonstrate the origin of spectral variations in background light emission of surface enhanced resonance hyper Raman scattering (SERHRS) from single Ag nanoaggregates. Ag nanoaggregate-by-nanoaggregate variations in background light emission spectra are related to plasma (plasmon) resonance spectra. Temporal variations in background light emission spectra with temporal blueshifts in plasma resonance spectra are also observed under continuous laser excitation. Both types of the variations in background light emission are reproduced by multiplying background light emission spectra measured from a Ag microaggregate by Lorentz function spectra derived from plasma resonance spectra. The reproduction reveals that second electromagnetic (EM) enhancement by plasma resonance is the origin of the variations. Additionally, spectral variations in background light emission of SERHRS are similar to that of surface enhanced resonance Raman scattering (SERRS). The similarity indicates that both types of background light emission commonly obtain second EM enhancement from identical plasma resonance. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3489920]
• Blinking Suppression in CdSe/ZnS Single Quantum Dots by TiO2 Nanoparticles

  Morihiko Hamada, Shunsuke Nakanishi, Tamitake Itoh, Mitsuru Ishikawa, Vasudevanpillai Biju

  ACS NANO 4 8 4445 - 4454 2010年08月 [査読有り][通常論文]
   

  The photoluminescence of semiconductor quantum dots and fluorescence of single molecules intermittently turn ON and OFF, a phenomenon referred to as blinking. In quantum dots, blinking occurs as a result of intermittent Auger ionization, which results in the formation of positively charged quantum dots. Due to strong Coulombic interactions, successive photoactivation of a charged quantum dot results in nonradiative carrier recombination, inducing long-lived OFF states in the intensity trajectories. Blinking is an undesirable property with respect to applications of quantum dots toward single-molecule imaging and single-photon logic devices. Here we report significant blinking suppression for CdSe/ZnS single quantum dots in the presence of TiO2 nanoparticles. In this work, we continuously recorded photoluminescence intensity trajectories of single quantum dots with and without TiO2 nanoparticles. Interestingly, the intensity trajectory of a single quantum dot that was covalently tethered on a cover glass and dipped in water resulted in near-complete blinking suppression as soon as a TiO2 nanoparticle solution was introduced. The blinking suppression was associated with a decrease in the photoluminescence intensity but without considerable changes in the photoluminescence lifetime, indicating that nonradiative carrier recombination in quantum dots was channeled into electron transfer to TiO2 nanoparticles and back electron transfer to quantum dots. On the basis of these experiments and recent reports on photoinduced electron transfer from quantum dots to TiO2 nanoparticles, we hypothesize that blinking of a quantum dot can be suppressed by increasing the rate of nonradiative regeneration of its neutral state by interfacing with a well-defined charge carrier trap such as an electron acceptor, which accepts an electron during Auger ionization and neutralizes the charged quantum dot by back electron transfer. Correlation between blinking suppression and electron transfer in a quantum dot-TiO2 nanoparticle system may have important implications, for the preparation of nonblinking quantum dot for incessant and on-demand light emission, donor-acceptor systems for efficient solar energy harvesting, and hybrid semiconductor materials for quantum optical devices.
• Bioconjugated quantum dots for cancer research: Present status, prospects and remaining issues

  Vasudevanpillai Biju, Sathish Mundayoor, Ramakrishnapillai V. Omkumar, Abdulaziz Anas, Mitsuru Ishikawa

  BIOTECHNOLOGY ADVANCES 28 2 199 - 213 2010年03月 [査読有り][通常論文]
   

  Semiconductor quantum dots (QDs) are nanoparticles in which charge carriers are three dimensionally confined or quantum confined. The quantum confinement provides size-tunable absorption bands and emission color to QDs. Also, the photoluminescence (PL) of QDs is exceptionally bright and stable, making them potential candidates for biomedical imaging and therapeutic interventions. Although fluorescence imaging and photodynamic therapy (PDT) of cancer have many advantages over imaging using ionizing radiations and chemo and radiation therapies, advancement of PDT is limited due to the poor availability of photostable and NIR fluorophores and photosensitizing (PS) drugs. With the introduction of biocompatible and NIR QDs, fluorescence imaging and PDT of cancer have received new dimensions and drive. In this review, we summarize the prospects of QDs for imaging and PDT of cancer. Specifically, synthesis of visible and NIR QDs. targeting cancer cells with QDs, in vitro and in vivo cancer imaging. multimodality, preparation of QD-PS conjugates and their energy transfer, photosensitized production of reactive oxygen intermediates (1101), and the prospects and remaining issues in the advancement of QD probes for imaging and PDT of cancer are summarized. (C) 2009 Elsevier Inc. All rights reserved.
• Quantitative evaluation of electromagnetic enhancement in surface-enhanced resonance Raman scattering from plasmonic properties and morphologies of individual Ag nanostructures

  Ken-ichi Yoshida, Tamitake Itoh, Hiroharu Tamaru, Vasudevanpillai Biju, Mitsuru Ishikawa, Yukihiro Ozaki

  PHYSICAL REVIEW B 81 11 2010年03月 [査読有り][通常論文]
   

  The electromagnetic (EM) enhancement in surface-enhanced resonance Raman scattering (SERRS) is quantitatively evaluated for rhodamine molecules adsorbed on Ag nanostructures. Polarization dependence of the plasma resonance (plasmon resonance) and the SERRS spectra from single isolated Ag nanostructures was evaluated to determine one-to-one relationship between optical anisotropy of plasma resonance, that of SERRS, and the morphology of the nanostructures. Experimental observations were compared with finite-difference time-domain calculations of the EM field induced by plasma resonance using individual morphology of the nanostructures. The experimental enhancement factor of SERRS similar to 10(9) was consistent with that of the calculations within a factor of similar to 2 for three excitation wavelengths. We conclusively fortify the indispensible importance of SERRS-EM theory with our results to design metal nanostructures generating strong EM enhancement.
• Modulatory role of versons glands peptide in insect metamorphosis

  Muraleedharan Damodaran, Gayathri E. Uma, R. V. Omkumar, Vasudevanpillai Biju, Govindan Bhaskaran

  ENDOCRINE JOURNAL 57 S612 - S612 2010年03月 [査読有り][通常論文]
  
• Selective Detection of HbA1c Using Surface Enhanced Resonance Raman Spectroscopy

  Manikantan Syamala Kiran, Tamitake Itoh, Ken-ichi Yoshida, Nagako Kawashima, Vasudevanpillai Biju, Mitsuru Ishikawa

  ANALYTICAL CHEMISTRY 82 4 1342 - 1348 2010年02月 [査読有り][通常論文]
   

  In the current work, we report on selective detection of RbA1c, a marker for glycemic control in diabetic patients, using surface enhanced resonance raman spectroscopy (SERRS). We found a characteristic band around 770-830 cm(-1) in the SERRS spectrum of HbA1c which was not present in the SERRS spectrum of HbA. To examine the contribution of glucosyl moiety to the characteristic SERRS band of RbA1c, we investigated SERRS spectra for nonenzymatically glycosylated HbA. We found that the SERRS spectral features are essentially identical for both HbA1c and nonenzymatically glycosylated HbA. Furthermore, addition of HbA into colloidal solution of silver nanoparticles (Ag NPs) resulted in the formation of large aggregates of Ag NPs and subsequent sedimentation. On the other hand, aggregation of Ag NPs was considerably low in the case of RbA1c. The differential effect of HbA and HbA1c on colloidal solution of Ag NPs, probably due to their difference in hydrophilicity, enabled us to separate them in a mixture. The separation was characterized by electrophoresis and SERRS analysis. Thus, colloidal solution of Ag NPs and SERRS would be a promising tool for the selective detection of HbA1c.
• Single-Molecule FRET Imaging for Enzymatic Reactions at High Ligand Concentrations

  Mitsuhiro Sugawa, So Nishikawa, Atsuko Hikikoshi Iwane, Vasudevanpillai Biju, Toshio Yanagida

  SMALL 6 3 346 - 350 2010年02月 [査読有り][通常論文]
  
• Reversible Dimerization of EGFR Revealed by Single-Molecule Fluorescence Imaging Using Quantum Dots

  Nagako Kawashima, Kenichi Nakayama, Kohji Itoh, Tamitake Itoh, Mitsuru Ishikawa, Vasudevanpillai Biju

  CHEMISTRY-A EUROPEAN JOURNAL 16 4 1186 - 1192 2010年 [査読有り][通常論文]
   

  The current work explores intermolecular interactions involved in the lateral propagation of cell-signaling by epidermal growth factor receptors (EGFRs). Activation of EGFRs by binding an EGF ligand in the extracellular domain of the EGFR and subsequent dimerization of the EGFR initiates cell-signaling. We investigated interactions between EGFRs in living cells by using single-molecule microscopy, Forster resonance energy transfer (FRET), and atomic force microscopy. By analyzing time-correlated intensity and propagation trajectories of quantum dot (QD)-labeled EGFR single molecules, we found that signaling dimers of EGFR [(EGF-EGFR)(2)] are continuously formed in cell membrane through reversible association of heterodimers [EGF(EGFR)(2)]. Also, we found that the lateral propagation of EGFR activation takes place through transient association of a heterodimer with predimers [(EGFR)(2)]. We varified the transient association between activated EGFR and predimers using FRET from QD-labeled heterodimers to Cy5-labeled predimers and correlated topography and fluorescence imaging. Without extended single-molecule fluorescence imaging and by using bio-conjugated QDs, reversible receptor dimerization in the lateral activation of EGFR remained obscured.
• Delivering quantum dots to cells: bioconjugated quantum dots for targeted and nonspecific extracellular and intracellular imaging

  Vasudevanpillai Biju, Tamitake Itoh, Mitsuru Ishikawa

  CHEMICAL SOCIETY REVIEWS 39 8 3031 - 3056 2010年 [査読有り][通常論文]
   

  Bioconjugated nanomaterials offer endless opportunities to advance both nanobiotechnology and biomedical technology. In this regard, semiconductor nanoparticles, also called quantum dots, are of particular interest for multimodal, multifunctional and multiplexed imaging of biomolecules, cells, tissues and animals. The unique optical properties, such as size-dependent tunable absorption and emission in the visible and NIR regions, narrow emission and broad absorption bands, high photoluminescence quantum yields, large one-and multi-photon absorption cross-sections, and exceptional photostability are the advantages of quantum dots. Multimodal imaging probes are developed by interfacing the unique optical properties of quantum dots with magnetic or radioactive materials. Besides, crystalline structure of quantum dots adds scope for high-contrast X-ray and TEM imaging. Yet another unique feature of a quantum dot is its spacious and flexible surface which is promising to integrate multiple ligands and antibodies and construct multi-functional probes for bioimaging. In this critical review, we will summarize recent advancements in the preparation of biocompatible quantum dots, bioconjugation of quantum dots, and applications of quantum dots and their bioconjugates for targeted and nonspecific imaging of extracellular and intracellular proteins, organelles and functions (181 references).
• In vitro imaging of cells using peptide-conjugated quantum dots

  Mitsuru Ishikawa, Vasudevanpillai Biju

  COLLOIDAL QUANTUM DOTS FOR BIOMEDICAL APPLICATIONS V 7575 2010年 [査読有り][通常論文]
   

  Efficient intracellular delivery of quantum dots (QDs) in living cells and elucidating the mechanism of the delivery are essential for advancing the applications of QDs to in vivo imaging and in vivo photodynamic therapy. Here, we demonstrate that clathrin-mediated endocytosis is the most dominant pathway for the delivery of peptide-conjugated QDs. We selected an insect neuropeptide, allatostatin (AST1), conjugated with CdSe-ZnS QDs, and investigated the delivery of the conjugate in living cells. We evaluated the contributions of clathrin-mediated endocytosis, receptor-mediated endocytosis, and charge-based cell penetration to the delivery of QD605-AST1 conjugates by flow cytometry and fluorescence video microscopy. The delivery was suppressed by similar to 57% in inhibiting phosphoinositide 3-kinase with wortmannin, which blocks the formation of clathrin-coated vesicles, and by similar to 45% in incubating the cells at 4 degrees C. Also, we identified clathrin-mediated endocytosis by two-color experiment to find colocalization of QD560-labeled clathrin heavy-chain antibody and QD605-AST1. We further observed reduction of the galanin receptor-mediated delivery of QD605-AST1 by similar to 8% in blocking the cells with a galanin antagonist, and reduction of charge-based cell penetration delivery by similar to 30% in removing the positive charge from arginine in the peptide and suppressing the cell-surface negative charge from glycosaminoglycan.
• In vitro imaging of cells using peptide-conjugated quantum dots

  Mitsuru Ishikawa, Vasudevan Biju

  Progress in Biomedical Optics and Imaging - Proceedings of SPIE 7575 2010年 [査読有り][通常論文]
   

  Efficient intracellular delivery of quantum dots (QDs) in living cells and elucidating the mechanism of the delivery are essential for advancing the applications of QDs to in vivo imaging and in vivo photodynamic therapy. Here, we demonstrate that clathrin-mediated endocytosis is the most dominant pathway for the delivery of peptide-conjugated QDs. We selected an insect neuropeptide, allatostatin (AST1), conjugated with CdSe-ZnS QDs, and investigated the delivery of the conjugate in living cells. We evaluated the contributions of clathrin-mediated endocytosis, receptormediated endocytosis, and charge-based cell penetration to the delivery of QD605-AST1 conjugates by flow cytometry and fluorescence video microscopy. The delivery was suppressed by ~57% in inhibiting phosphoinositide 3-kinase with wortmannin, which blocks the formation of clathrin-coated vesicles, and by ~45% in incubating the cells at 4°C. Also, we identified clathrin-mediated endocytosis by two-color experiment to find colocalization of QD560-labeled clathrin heavy-chain antibody and QD605-AST1. We further observed reduction of the galanin receptor-mediated delivery of QD605-AST1 by ~8% in blocking the cells with a galanin antagonist, and reduction of charge-based cell penetration delivery by ~30% in removing the positive charge in the peptide from arginine and suppressing the cell-surface negative charge from glycosaminoglycan. © 2010 Copyright SPIE - The International Society for Optical Engineering.
• Spectral shapes of surface-enhanced resonance Raman scattering sensitive to the refractive index of media around single Ag nanoaggregates

  Ken-ichi Yoshida, Tamitake Itoh, Vasudevanpillai Biju, Mitsuru Ishikawa, Yukihiro Ozaki

  APPLIED PHYSICS LETTERS 95 26 2009年12月 [査読有り][通常論文]
   

  We found large spectral changes in surface-enhanced resonance Raman scattering (SERRS) with increasing refractive index of media around single Ag nanoaggregates. We analyzed relationship between the spectral changes in SERRS and those in plasma (plasmon) resonance based on the twofold electromagnetic (EM) enhancement theory. The analysis revealed that the changes in SERRS spectra are induced by changes in spectral shapes of twofold EM enhancement factors, which arise from coupling of plasma resonance with both incident and Raman scattering light.
• Photoluminescence of CdSe Quantum Dots: Shifting, Enhancement and Blinking

  Vasudevanpillai Biju, Mitsuru Ishikawa

  Molecular Nano Dynamics: Vol. I: Spectroscopic Methods and Nanostructures / Vol. II: Active Surfaces, Single Crystals and Single Biocells 1 293 - 314 2009年11月27日 [査読有り][通常論文]
  
• Imaging the cell wall of living single yeast cells using surface-enhanced Raman spectroscopy

  Athiyanathil Sujith, Tamitake Itoh, Hiroko Abe, Ken-ichi Yoshida, Manikantan S. Kiran, Vasudevanpillai Biju, Misturu Ishikawa

  ANALYTICAL AND BIOANALYTICAL CHEMISTRY 394 7 1803 - 1809 2009年08月 [査読有り][通常論文]
   

  The surface of a living yeast cell (Saccharomyces cerevisiae strain W303-1A) has been labeled with silver (Ag) nanoparticles that can form nanoaggregates which have been shown to have surface-enhanced Raman scattering (SERS) activity. The cell wall of a single living yeast cell has been imaged by use of a Raman microspectroscope. The SERS spectra measured from different Ag nanoaggregates were found to be different. This can be explained on the basis of detailed spectral interpretation. The SERS spectral response originates from mannoproteins which cover the outermost regions of the yeast cell wall. Analysis of SERS spectra from the cell wall and the extracted mannoproteins from the yeast has been performed for the clarification of variation in SERS spectra.
• Spontaneous Adsorption on a Hydrophobic Surface Governed by Hydrogen Bonding

  Fuquan Dang, Takeshi Hasegawa, Vasudevanpillai Biju, Mitsuru Ishikawa, Noritada Kaji, Takao Yasui, Yoshinobu Baba

  LANGMUIR 25 16 9296 - 9301 2009年08月 [査読有り][通常論文]
   

  Spontaneous adsorption from solution onto solid surface is a common phenomenon in nature, but the force that governs adsorption is still a matter of considerable debate. (1,2) We found that surfactants and cellulose adsorb from solution onto a poly(methyl methacrylate) (PMMA) surface in an ordered and cooperative way governed by hydrogen bonding. The glucose rings of n-dodecyl-beta-D-maltoside (DDM) and hydroxyethylcellulose (HEC) stand perpendicular to the surface, H-bond to the surface COOMe groups with their C=O and Me-O bonds parallel to the surface, and form a tight monolayer. The non-H-bonded COOMe groups orient their C=O bonds perpendicular to the surface. In contrast, the glucose rings of hydrophobically modified hydroxyethylcellulose (HMHEC) lie flat with the side chains perpendicular to the surface and H-bond to the perpendicular-oriented C=O groups. The non-H-bonded COOMe groups orient their C=O bonds parallel but Me-O bonds near-perpendicular to the surface for stabilizing HMHEC. The current work provides a detailed picture of how surface-active molecules interact with a solid surface and self-assemble into greatly different architectures.
• Clathrin-Mediated Endocytosis of Quantum Dot-Peptide Conjugates in Living Cells

  Abdulaziz Anas, Tetsuya Okuda, Nagako Kawashima, Kenichi Nakayama, Tamitake Itoh, Mitsuru Ishikawa, Vasudevanpillai Biju

  ACS NANO 3 8 2419 - 2429 2009年08月 [査読有り][通常論文]
   

  Efficient intracellular delivery of quantum dots (QDs) and unravelling the mechanism underlying the intracellular delivery are essential for advancing the applications of QDs toward in vivo imaging and therapeutic interventions. Here, we show that clathrin-mediated endocytosis is the most important pathway for the intracellular delivery of peptide-conjugated QDs. We selected an insect neuropeptide, namely, allatostatin (AST1, APSGAQRLYG FGL-NH(2)), conjugated it with CdSe-ZnS QDs, and investigated the intracellular delivery of the conjugate in living cells such as human epidermoid ovarian carcinoma cells (A431) and mouse embryonic fibroblast cells (3T3). We selected AST1 to investigate the intracellular delivery of US because we recently found it to be efficient for delivering US in living mammalian cells. Also, the receptors of AST1 in insects show functional and sequence similarity to G-protein-coupled galanin receptors in mammals. We employed flow cytometry and fluorescence microscopy and investigated the contributions of clathrin-mediated endocytosis, receptor-mediated endocytosis, and charge-based cell penetration or transduction to the Intracellular delivery of QD-AST1 conjugates. Interestingly, the intracellular delivery was suppressed by similar to 57% when we inhibited the regulatory enzyme phosphoinositide 3-kinase (PI3K) with wortmannin and blocked the formation of clathrin-coated vesicles. In parallel, we investigated clathrin-mediated endocytosis by colocalizing QD560-labeled clathrin heavy-chain antibody and QD605-AST1. We also estimated galanin receptor-mediated endocytosis of QD-AST1 at <10% by blocking the cells with a galanin antagonist and transduction at <30% by both removing the charge of the peptide due to arginine and suppressing the cell-surface charge due to glycosaminoglycan. In short, the current work shows that multiple pathways are involved in the intracellular delivery of peptide-conjugated Us, among which clathrin-mediated endocytosis is the most important.
• Surface Plasmon Excitation and Surface-Enhanced Raman Scattering Using Two-Dimensionally Close-Packed Gold Nanoparticles

  Mohammad Kamal Hossain, Yasutaka Kitahama, Vasudevanpillai Biju, Tamitake Itoh, Tadaaki Kaneko, Yukihiro Ozaki

  JOURNAL OF PHYSICAL CHEMISTRY C 113 27 11689 - 11694 2009年07月 [査読有り][通常論文]
   

  We investigated plasmon excitation and surface-enhanced Raman scattering (SERS) of crystal violet dye adsorbed on two-dimensionally (2D) close-packed gold nanostructures. With reference to the absorption maximum of colloidal nanoparticles, the 2D nanostructures showed red-shifted maxima at similar to 560 and 740 nm. Interestingly, we found that the surface plasmon resonance (SPR) and SERS signals were preferentially enhanced near the edge of the 2D nanostructures. Both the SPR and SERS images suggest good correlation between the SPR-mediated localized electromagnetic field and the localized optical field, particularly near the edge of the 2D nanostructures. We observed broad SPR bands near the edge and red-shifted and intense bands near the center of the 2D nanostructures. Also, the overall SERS enhancement on the 2D nanostructures was comparable to that reported on engineered gold nanostructures. The integral SERS intensity near the edge was higher than that measured near the center. We carried out finite-different time-domain simulations and demonstrated that the experimental data are consistent with the simulated ones. Here, several proximal localization sites appeared for nanoparticles with their out-of-plane polarization parallel to the interparticle axis. Thus, the experimental results and the simulation predicted the existence of multipolar plasmon excitation and a narrow passage for energy percolation, which are often obscured in ensemble SERS measurements.
• Evaluation of electromagnetic enhancement of surface enhanced hyper Raman scattering using plasmonic properties of binary active sites in single Ag nanoaggregates

  Tamitake Itoh, Hiroyuki Yoshikawa, Kenichi Yoshida, Vasudevanpillai Biju, Mitsuru Ishikawa

  JOURNAL OF CHEMICAL PHYSICS 130 21 2009年06月 [査読有り][通常論文]
   

  We found a binary active site of surface enhanced Raman scattering (SERS) and surface enhanced hyper Raman scattering (SEHRS) in single Ag nanoaggregates by single particle spectroscopy. The intensity fluctuation of SEHRS was canceled by dividing SEHRS intensity by SERS intensity on the basis of the binary active site analysis. Thanks to the identification of the plasmons common to both SERS and SEHRS we revealed that an enormous enhancement in SEHRS is ascribed to the electromagnetic (EM) enhancement entirely coupled with longitudinal plasmon modes excluding other kinds of enhancement factors. Our results indicate that EM enhancement factors of metal nanostructures are estimated from spectral information on the longitudinal plasmon resonance band obtained by the scattering or absorption spectra of the nanostructures.
• A Novel Technique To Investigate the Decondensation of pc-DNA3.1-luc in Nuclear Sub-Domain with QD-FRET

  Sharif M. Shaheen, Hidetaka Akita, Atsushi Yamashita, Ryo Katoono, Nobuhiko Yui, Vasudevanpillai Biju, Mitsuru Ishikawa, Hideyoshi Harashima

  MOLECULAR THERAPY 17 S330 - S330 2009年05月 [査読有り][通常論文]
  
• Optical force enhanced by plasmon resonance allowing position-sensitive synthesis and immobilization of single Ag nanoparticles on glass surfaces

  Tamitake Itoh, Vasudevanpillai Biju, Mitsuru Ishikawa, Syoji Ito, Hiroshi Miyasaka

  APPLIED PHYSICS LETTERS 94 14 2009年04月 [査読有り][通常論文]
   

  Focused laser light in an aqueous solution of silver nitrate and disodium citrate allowed the synthesis and immobilization of single Ag particles on a glass surface. The as-synthesized Ag particles were free from aggregation. Rayleigh scattering spectra of the Ag particles showed a plasmon resonance band at similar to 490 nm. Analysis of the spectra revealed that the Ag particles have oblate-spindle shapes with similar to 30 nm diameter. The polarizability of the Ag nanoparticles demonstrated that soon after the formation of the particles at the focal point, optical force repels them out of the focal point and immobilizes on the glass surface.
• Experimental evaluation of the twofold electromagnetic enhancement theory of surface-enhanced resonance Raman scattering

  Ken-ichi Yoshida, Tamitake Itoh, Vasudevanpillai Biju, Mitsuru Ishikawa, Yukihiro Ozaki

  PHYSICAL REVIEW B 79 8 2009年02月 [査読有り][通常論文]
   

  We examined an electromagnetic (EM) theory of surface-enhanced resonance Raman scattering (SERRS) using single Ag nanoaggregates. The SERRS-EM theory is characterized by twofold EM enhancement induced by the coupling of plasmon resonance with both excitation and emission of Raman scattering plus fluorescence. The total emission cross-section spectra of enhanced Raman scattering and enhanced fluorescence were calculated using the following parameters: the spectrum of enhancement factor induced by plasmon resonance, resonance Raman scattering overlapped with fluorescence, and excitation wavelengths. The calculations well agreed with experimental total emission cross-section spectra, thus providing strong indications that the SERRS-EM theory is quantitatively correct.
• 2TP2-05 Trans-membrane delivery of semiconductor quantum dots in living cells(The 47th Annual Meeting of the Biophysical Society of Japan)

  Biju Vasudevanpillai, Anas Abdulaziz, Okuda Tetsuya, Itoh Tamitake, Ishikawa Mitsuru

  生物物理 49 S48  一般社団法人 日本生物物理学会 2009年
• 2P-071 Surface enhanced resonance raman scattering of HbA and HbA1c : Implications for diabetic diagnosis(Heme proteins,The 47th Annual Meeting of the Biophysical Society of Japan)

  Kiran Manikantan Syamala, Itoh Tamitake, Yoshida Kenichi, Kawashima Nagako, Biju Vasudevanpillai, Ishikawa Mitsuru

  生物物理 49 S117  一般社団法人 日本生物物理学会 2009年
• Semiconductor quantum dots and metal nanoparticles: syntheses, optical properties, and biological applications

  Vasudevanpillai Biju, Tamitake Itoh, Abdulaziz Anas, Athiyanathil Sujith, Mitsuru Ishikawa

  ANALYTICAL AND BIOANALYTICAL CHEMISTRY 391 7 2469 - 2495 2008年08月 [査読有り][通常論文]
   

  We review the syntheses, optical properties, and biological applications of cadmium selenide (CdSe) and cadmium selenide-zinc sulfide (CdSe-ZnS) quantum dots (QDs) and gold (Au) and silver (Ag) nanoparticles (NPs). Specifically, we selected the syntheses of QDs and Au and Ag NPs in aqueous and organic phases, size- and shape-dependent photoluminescence (PL) of QDs and plasmon of metal NPs, and their bioimaging applications. The PL properties of QDs are discussed with reference to their band gap structure and various electronic transitions, relations of PL and photoactivated PL with surface defects, and blinking of single QDs. Optical properties of Ag and Au NPs are discussed with reference to their size- and shape-dependent surface plasmon bands, electron dynamics and relaxation, and surface-enhanced Raman scattering (SERS). The bioimaging applications are discussed with reference to in vitro and in vivo imaging of live cells, and in vivo imaging of cancers, tumor vasculature, and lymph nodes. Other aspects of the review are in vivo deep tissue imaging, multiphoton excitation, NIR fluorescence and SERS imaging, and toxic effects of NPs and their clearance from the body.
• Photosensitized breakage and damage of DNA by CdSe-ZnS quantum dots

  AbdulAziz Anas, Hidetaka Akita, Hideyoshi Harashima, Tamitake Itoh, Mitsuru Ishikawa, Vasudevanpillai Biju

  JOURNAL OF PHYSICAL CHEMISTRY B 112 32 10005 - 10011 2008年08月 [査読有り][通常論文]
   

  Strand breakages and nucleobase damages in plasmid DNA (pDNA) by CdSe-ZnS quantum dots (QDs) are investigated under different conditions of photoactivation. Here, streptavidin functionalized CdSe-ZnS QDs are conjugated to biotinylated pDNA, and photosensitized strand breakages and nucleobase damages in the conjugates are investigated using atomic force microscopy (AFM) imaging, gel electrophoreses analyses, and assay of reactive oxygen intermediates (ROI). Also, reactions of photoactivated pDNA-QD conjugates with base excision repair enzymes such as formamidopyrimidine glycosylase (Fpg) and endonuclease III (Endo 111) show damages of purine and pyrimidine bases. The base excision repair enzymes recognize and remove the damaged bases. The base excision reactions of photoactivated pDNA-QD conjugates resulted in pDNA strand breakages, which appeared as sheared bands in agarose gel images. On the basis of AFM imaging, reactions of Fpg and Endo III with damaged pDNA, ROI assay, and literature reports, we attribute the breakage and damage of pDNA to its reactions with ROI. The production of ROI by photoactivated QDs is confirmed by nitroblue tetrazolium (NBT) assay. The current work shows that photoactivation of QD-conjugated nucleic acids for an extended period of time is not favorable for their stability. On the other hand, photoinduced production of ROI by QDs is an emerging research area with potential applications in the photodynamic therapy of cancer. In this regard, photosensitized damage of pDNA observed in the current work shows possibilities of QDs in nucleus-targeted photodynamic therapy.
• Relations between dewetting of polymer thin films and phase-separation of encompassed quantum dots

  Ryodai Kanemoto, Abdulaziz Anas, Yusuke Matsumoto, Rintaro Ueji, Tamitake Itoh, Yoshinobu Baba, Shunsuke Nakanishi, Mitsuru Shikawa, Vasudevanpillai Biju

  JOURNAL OF PHYSICAL CHEMISTRY C 112 22 8184 - 8191 2008年06月 [査読有り][通常論文]
   

  Incorporation of semiconductor quantum dots (QDs) at high densities in polymer thin films is promising for the development of nanoscale sensors, light-emitting diodes, and photovoltaic devices. However, inhomogeneous distribution and aggregation of QDs in polymers limit the applications of QD-polymer composites. We investigated the origin of the aggregation of CdSe-ZnS QDs in polybutadiene (PB) thin films and its relations with the dewetting of polymer thin films on inorganic surfaces. Microscale dewetting of PB thin films on glass surfaces resulted in the formation of honeycomb structures of PB, and nanoscale dewetting on the QD surface resulted in phase-separation and aggregation of QDs. The formation of the honeycomb structures of PB is attributed to phase-separation between PB and glass during the dewetting on the glass surface, and the aggregation of QDs is attributed to the phase-separation between PB and QDs during the dewetting on the QD surface. The honeycomb structures of PB are characterized using optical microscopy and atomic force microscopy (AFM) imaging, and the phase-separation and aggregation of QDs are characterized using transmission electron microscopy (TEM) imaging and inter-QD Forster resonance energy-transfer (FRET). FRET is confirmed from photoluminescence (PL) spectral shifts and decreases of PL intensity and lifetime of QDs. Without the phase-separation and aggregation of QDs, inter-QD FRET is unexpected under the selected densities of QDs; the calculated inter-QD distance (>60 nm) for a homogeneous distribution of QDs is beyond the Forster distance (<10 nm). The phase-separation and aggregation of QDs in PB thin films are further characterized based on a decrease of FRET from QD to rhodamine 590 (R590) with an increase in the density of QDs. The aggregation of QDs occurs because of the rejection of QDs by PB molecules during the release of recoiling energy, which is distributed among entangled polymer chains and between polymer chains and QDs in the thin films. In the current work, we characterized the nanoscale dewetting of PB on the surface of QDs, the phase-separation and aggregation of QDs in PB thin films, and the limit of close-packing of QDs in polymer thin films without aggregation that are valuable during the construction of QD and polymer-based thin-film devices.
• Surface enhanced Raman scattering analyses of individual silver nanoaggregates on living single yeast cell wall

  Athiyanathil Sujith, Tamitake Itoh, Hiroko Abe, Abdul Aziz Anas, Kenichi Yoshida, Vasudevanpillai Biju, Mitsuru Ishikawa

  APPLIED PHYSICS LETTERS 92 10 2008年03月 [査読有り][通常論文]
   

  We labeled the living yeast cell surface (Saccharomyces cerevisiae strain W303-1A) by silver nanoparticles which can form nanoaggregates and found to show surface enhanced Raman scattering (SERS) activity. Blinking of SERS and its polarization dependence reveal that SERS signals are from amplified electromagnetic field at nanometric Ag nanoparticles gaps with single or a few molecules sensitivity. We tentatively assigned SERS spectra from a yeast cell wall to mannoproteins. Nanoaggregate-by-nanoaggregate variations and temporal fluctuations of SERS spectra are discussed in terms of inhomogeneous mannoprotein distribution on a cell wall and possible ways of Ag nanoaggregate adsorption, respectively. (C) 2008 American Institute of Physics.
• Photoluminescence quenching and intensity fluctuations of CdSe-ZnS quantum dots on an Ag nanoparticle film

  Yuusuke Matsumoto, Ryodai Kanemoto, Tamitake Itoh, Shunsuke Nakanishi, Mitsuru Ishikawa, Vasudevanpillai Biju

  JOURNAL OF PHYSICAL CHEMISTRY C 112 5 1345 - 1350 2008年02月 [査読有り][通常論文]
   

  Intermittent "on" and "off (blinking) photoluminescence (PL) of single-CdSe/ZnS quantum dots (QDs) is modified when placed on an Ag nanoparticle (NP) film into stochastic fluctuations with nonzero intensity "off" (pseudo off) periods. Also, the PL quantum efficiency (from 0.42 to 0.22) and lifetime (from 5.2 to 1.5 ns) of QDs are considerably decreased at ensemble level in the presence of Ag NPs, and a histogram of the PL lifetime of single-QDs is shifted (from 4.2 to 1.7 ns) and tapered (full width at half-maximum from 3.3 to 1.1 ns) when placed on an Ag NP film. The quenching of the PL quantum efficiency and decrease of the PL lifetime are attributed to ultrafast energy transfer from photoexcited QDs to Ag NPs. The energy-transfer process competes with exciton relaxations and influences carrier trapping in surface defect-states (band gap defects) and Auger relaxation, which are considered to be the origins of blinking. The contribution of surface-states on the modified PL was identified from decreased contribution of a slow component to the PL decays of ensemble- and single-QDs in the presence of Ag NPs. On the basis of ensemble averaged PL intensity and lifetime and single-QD lifetime and intensity trajectory analyses, we propose that the energy-transfer process from photoexcited QDs to Ag NPs result a redistribution of relaxation processes and provide fluctuating trajectories with nonzero intensities to single-QDs. Apart from the observations of modified blinking and narrow lifetime distribution of QDs, the current work partially supports a model proposed by Markus and co-workers that blinking is related to localization of charge carriers in defects.
• Optical and dynamic properties of water-soluble highly luminescent CdTe quantum dots

  Abhijit Mandal, Junichi Nakayama, Naoto Tamai, Vasudevanpillai Biju, Mitsuru Isikawa

  JOURNAL OF PHYSICAL CHEMISTRY B 111 44 12765 - 12771 2007年11月 [査読有り][通常論文]
   

  CdTe quantum dots (QDs) were synthesized in aqueous solution using thioglycolic acid (HS-CH2COOH, TGA) as a stabilizer. The phenomenon of "on" and "off" luminescence intermittency (blinking) of CdTe QDs in PVA and trehalose was investigated by single-molecule optical microscopy, and we identified that the intermittencies of single QDs were correlated with the interaction of water molecules absorbed on the QD surface. The "off' times, the interval between adjacent "on" states, remained essentially unaffected with an increase in excitation intensity. Every QD showed a similar power law behavior for the "off" time distribution regardless of the excitation intensity and aqueous environment of the QDs;. In the case of "on" time distribution, power law behavior with an exponential cutoff tail is observed at longer time scales. The time traces indicated that the "on" time was inversely proportional to the excitation intensity; the duration of "on" time became shorter with increasing excitation intensity. An increase in the duration of "on" time was observed in trehalose with respect to that in PVA. We obtained a clear decrease in the power law exponent when PVA was replaced with trehalose. These observations indicate that the luminescence blinking statistics of water-soluble single CdTe QDs is significantly dependent on the aqueous environment, which is interpreted in terms of passivation of the surface trap states of QDs.
• Second enhancement in surface-enhanced resonance Raman scattering revealed by an analysis of anti-Stokes and Stokes Raman spectra (vol 76, pg 085405, 2007)

  Tamitake Itoh, Kenichi Yoshida, Vasudevanpillai Biju, Yasuo Kikkawa, Mitsuru Ishikawa, Yukihiro Ozaki

  PHYSICAL REVIEW B 76 12 2007年09月 [査読有り][通常論文]
  
• Quantum dot-insect neuropeptide conjugates for fluorescence imaging, transfection, and nucleus targeting of living cells

  Vasudevanpillai Biju, Damodaran Muraleedharan, Ken-ichi Nakayama, Yasuo Shinohara, Tamitake Itoh, Yoshinobu Baba, Mitsuru Ishikawa

  LANGMUIR 23 20 10254 - 10261 2007年09月 [査読有り][通常論文]
   

  We identified an insect neuropeptide, namely, allatostatin I from Drosophila melanogaster, that transfects living NIH 3T3 and A431 human epidermoid carcinoma cells and transports quantum dots (QDs) inside the cytoplasm and even the nucleus of the cells. QD-conjugated biomolecules are valuable resources for visualizing the structures and functions of biological systems both in vivo and in vitro. Here, we selected allatostatin 1, Ala-Pro-Ser-Gly-AlaGln-Arg-Leu-Tyr-Gly-Phe-Gly-Leu-NH2, conjugated to streptavidin-coated CdSe-ZnS QDs. This was followed by investigating the transfection of live mammalian cells with QD-allatostatin conjugates, the transport of QDs by allatostatin inside the nucleus, and the proliferation of cells in the presence of allatostatin. Also, on the basis of dose-dependent proliferation of cells in the presence of allatostatin we identified that allatostatin is not cytotoxic when applied at nanomolar levels. Considering the sequence similarity between the receptors of allatostatin in D. melanogaster and somatostatin/galanin in mammalian cells, we expected interactions and localization of allatostatin to somatostatin/galanin receptors on the membranes of 3T3 and A431 cells. However, with QD conjugation we identified that the peptide was delivered inside the cells and localized mainly to the cytoplasm, microtubules, and nucleus. These results indicate that allatostatin is a promising candidate for high-efficiency cell transfection and nucleus-specific cell labeling. Also, the transport property of allatostatin is promising with respect to label/drug/gene delivery and high contrast imaging of live cells and cell organelles. Another promising application of allatostatin is that the transport of QDs inside the nucleus would lift the limit of general photodynamic therapy to nucleus-specific photodynamic therapy, which is expected to be more efficient than photosensitization at the cell membrane or in the cytoplasm as a result of the short lifetime of singlet oxygen.
• Second enhancement in surface-enhanced resonance Raman scattering revealed by an analysis of anti-Stokes and Stokes Raman spectra

  Tamitake Itoh, Kenichi Yoshida, Vasudevanpillai Biju, Yasuo Kikkawa, Mitsuru Ishikawa, Yukihiro Ozaki

  Physical Review B - Condensed Matter and Materials Physics 76 8 2007年08月06日 [査読有り][通常論文]
   

  Evidence of "twofold" electromagnetic (EM) enhancement in surface-enhanced resonance Raman scattering (SERRS) that exhibits a SERRS enhancement factor of up to 1014 has been analyzed by comparing SERRS spectra and plasmon resonance Rayleigh scattering spectra. We identified that SERRS spectral variations are induced by selective enhancement of SERRS bands whose maxima are close to plasmon resonance maxima. The correlation between the selective enhancement of SERRS and the plasmon energy demonstrated that the variations in SERRS spectra are induced by second EM enhancement in SERRS as a result of coupling between scattering photons and plasmons. © 2007 The American Physical Society.
• COLL 494-Light and heat induced photoluminescence-variations in quantum dots

  Vasudevanpillai Biju, Tamitake Itoh, Mitsuru Ishikawa

  ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 234 2007年08月 [査読有り][通常論文]
  
• PHYS 525-Photoluminescence-variations of CdSe quantum dots and its relation to interactions of solvents and dissolved molecules on surface states

  Vasudevanpillai Biju, Tamitake Itoh, Mitsuru Ishikawa

  ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 234 2007年08月 [査読有り][通常論文]
  
• Second enhancement in surface-enhanced resonance Raman scattering revealed by an analysis of anti-Stokes and Stokes Raman spectra

  Tamitake Itoh, Kenichi Yoshida, Vasudevanpillai Biju, Yasuo Kikkawa, Mitsuru Ishikawa, Yukihiro Ozaki

  PHYSICAL REVIEW B 76 8 2007年08月 [査読有り][通常論文]
   

  Evidence of "twofold" electromagnetic (EM) enhancement in surface-enhanced resonance Raman scattering (SERRS) that exhibits a SERRS enhancement factor of up to 10(14) has been analyzed by comparing SERRS spectra and plasmon resonance Rayleigh scattering spectra. We identified that SERRS spectral variations are induced by selective enhancement of SERRS bands whose maxima are close to plasmon resonance maxima. The correlation between the selective enhancement of SERRS and the plasmon energy demonstrated that the variations in SERRS spectra are induced by second EM enhancement in SERRS as a result of coupling between scattering photons and plasmons.
• Photoinduced photoluminescence variations of CdSe quantum dots in polymer solutions

  Vasudevanpillai Biju, Ryodai Kanemoto, Yuusuke Matsumoto, Sayaka Ishii, Shunsuke Nakanishi, Tamitake Itoh, Yoshinobu Baba, Mitsuru Ishikawa

  JOURNAL OF PHYSICAL CHEMISTRY C 111 22 7924 - 7932 2007年06月 [査読有り][通常論文]
   

  Photoluminescence (PL) quantum efficiencies and lifetimes of CdSe quantum dots (QDs) were investigated under photoactivation in different chemical environments including polymer solutions and solvent systems. We observed considerable enhancement of the PL quantum efficiency of the QDs when photoactivated above the band gap in the presence of polymers such as poly(dimethyl siloxane) (PDMS), poly(vinyl pyrrolidone) (PVP), and poly(butadiene) (PBD). Furthermore, the PL spectra and the enhanced PL quantum efficiencies of the QDs were considerably stabilized under continuous photoactivation in the presence of dissolved polymers. Under photoactivation, the PL quantum efficiency was increased from 8% to 26-37% depending on the polymer environment. An increase of the PL quantum efficiency was also observed in solvents such as CHCl3 and n-butanol. However, photoactivation of the QDs in solvents with small dipole moments such as n-hexane and toluene resulted in substantial decreases of the PL quantum efficiency (from 8% to < 1%). The photoactivated PL intensity of the QDs was stable in the presence of polymers as a result of static passivation of QDs' surface. In general, the increase of the PL quantum efficiency of the QDs under photoactivation was associated with an increase of the average PL lifetime values (from similar to 7 to similar to 12 ns). On the other hand, the increase of the PL quantum efficiency (from 8% to 37%) of QDs in the presence of PVP was associated with a decrease of the average PL lifetime value (from 7.16 to 3.51 ns). From the PL variations of the CdSe QDs under continuous photoactivation in the presence of different polymers and solvents, we determined that static passivation of the surface defects by molecules in the environment plays an important role in the surface-related emission and stability of the photophysical properties of the QDs. The variations of the PL lifetimes and quantum efficiencies under different chemical environments were helpful not only in understanding the involvement of surface states in the deactivation processes of photoexcited QDs but also in identifying ideal polymers and solvents for photoinduced surface passivation of QDs.
• Combined spectroscopic and topographic characterization of nanoscale domains and their distributions of a redox protein on bacterial cell surfaces

  Vasudevanpillai Biju, Duohai Pan, Yuri A. Gorby, Jim Fredrickson, Jeff McLean, Daad Saffarini, H. Peter Lu

  LANGMUIR 23 3 1333 - 1338 2007年01月 [査読有り][通常論文]
   

  Redox protein nanoscale domains on the cell surface of a bacterium, Shewanella oneidensis MR1, grown in the absence and presence of electron acceptors, is topographically characterized using combined atomic force microscopy (AFM) and confocal surface enhanced Raman scattering (SERS) spectroscopy. The protruding nanoscale domains on the outer membrane of S. oneidensis were observed, as was their disappearance upon exposure to electron acceptors such as oxygen, nitrate, fumarate, and iron nitrilotriacetate (FeNTA). Using SERS spectroscopy, a redox heme protein was identified as a major component of the cell surface domains. This conclusion was further confirmed by the disappearance of Raman vibrational frequencies, characteristic of heme proteins, upon exposure of the cells to electron acceptors. Our experimental results from our AFM imaging and SERS spectroscopy, consistent with the literature, suggest the protruding nanoscale surface domains as heme-containing secretions. Our results on the distributions of redox proteins on microbial cell surfaces will be helpful for a mechanistic understanding of the behaviors of surface proteins and their interactions with redox environments.
• Chapter 10 Interaction between metal-free porphine and surface Ag atoms through temporal fluctuation of surface- enhanced resonance raman scattering and background- light emission

  Tamitake Itoh, Kazuhiro Hashimoto, Vasudevanpillai Biju, Mitsuru Ishikawa, Bayden R. Wood, Yukihiro Ozaki

  Handai Nanophotonics 3 161 - 174 2007年 [査読有り][通常論文]
  
• Quenching of photoluminescence in conjugates of quantum dots and single-walled carbon nanotube

  Vasudevanpillai Biju, Tamitake Itoh, Yoshinobu Baba, Mitsuru Ishikawa

  JOURNAL OF PHYSICAL CHEMISTRY B 110 51 26068 - 26074 2006年12月 [査読有り][通常論文]
   

  Development of quantum dot (QD) based device components requires controlled integration of QDs into different photonic and electronic materials. In this regard, introduction of methods for regular arrangement of QDs and investigation of properties of QD-based assemblies are important. In the current work we report (1) controlled conjugation of CdSe-ZnS QDs to sidewall-functionalized single-walled carbon nanotube (SWCNT) templates (2) and the effect of conjugation of QDs to SWCNT on the photoluminescence (PL) properties of QDs. We identified that PL intensity and lifetime of QDs are considerably reduced after conjugation to SWCNT. The origin of the quenching of the PL intensity and lifetime was discussed in terms of Forster resonance energy transfer (FRET). FRET involves nonradiative transfer of energy from a photoexcited QD (energy donor) to a nearby SWCNT (energy acceptor) in the ground state. This was examined by varying the density of QDs on SWCNT and conjugating smaller and bigger QDs to the same SWCNT. We estimated the FRET efficiency in QD-SWCNT conjugates from the quenching of the PL intensity and lifetime and identified that FRET is independent of the density and type of QDs on SWCNT but inherent to QD-SWCNT conjugates.
• Variations in steady-state and time-resolved background luminescence from surface-enhanced resonance Raman scattering-active single Ag nanoaggregates

  Tamitake Itoh, Yasuo Kikkawa, Vasudevanpillai Biju, Mitsuru Ishikawa, Akifumi Ikehata, Yukihiro Ozaki

  JOURNAL OF PHYSICAL CHEMISTRY B 110 43 21536 - 21544 2006年11月 [査読有り][通常論文]
   

  We observed a background luminescence emission that was associated with surface-enhanced resonance Raman scattering (SERRS) of rhodamine 6G (R6G) molecules adsorbed on single Ag nanoaggregates and investigated the origin of the background luminescence. Thanks to the observation of single nanoaggregates, we clearly identified nanoaggregate-by-nanoaggregate variations in the steady-state and time-resolved background luminescence spectra of each nanoaggregate. From the variations in the steady-state spectra, two kinds of key properties were revealed. First, the background luminescence spectra were divided into four components: one fluorescence band corresponding to the monomers of R6G and three Lorentzian bands whose maxima were red-shifted from the fluorescence maximum of the monomer by several tens of nanometers. On the basis of the red-shifted luminescence maxima, and experimental and theoretical studies of background luminescence, we attributed the three background luminescences to fluorescence from aggregates (dimer and two kinds of higher-order aggregates) of R6G molecules on an Ag surface. Second, a positive correlation was observed between wavelengths of background luminescence maxima and wavelengths of plasmon resonance maxima. This positive correlation invoked the idea that the dipoles of both the background luminescence and the plasmon radiation are coupled with each other. From the key observations in the steadystate background luminescence spectra, we propose that two factors contribute to the variations in the steadystate background luminescence spectra; one is the aggregation (monomer, dimer, and two kinds of higher-order aggregates) of R6G molecules on an Ag surface, and the other is plasmon resonance maxima of single Ag nanoaggregates. Considering these two factors, we propose that the variations in the time-resolved background luminescence spectra are associated with deaggregation of R6G molecules (higher- to lower-order aggregates) and temporal shifts in the plasmon resonance maxima of single Ag nanoaggregates.
• Close-conjugation of quantum dots and gold nanoparticles to sidewall functionalized single-walled carbon nanotube templates

  Vasudevanpillai Biju, Tamitake Itoh, Yoji Makita, Mitsuru Ishikawa

  JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY 183 3 315 - 321 2006年10月 [査読有り][通常論文]
   

  Two types of nanoscale hybrid materials have been synthesized by conjugating CdSe-ZnS quantum dots (QDs) and gold nanoparticles (NPs) to sidewall functionalized single-walled carbon nanotube (SWNT) templates, and examined photoluminescence (PL) properties of the hybrid materials. The two types of hybrid nanoscale materials are SWNT-QD and SWNT-gold-NP conjugates. Excessive sidewall functionalization of SWNT into nitro- and amino-derivatives provided weak PL and water solubility to the SWNT derivatives. Solubility of SWNT derivatives in aqueous media was helpful for efficient conjugation of SWNTs to QDs and gold-NPs. The SWNT-QD and SWNT-gold-NP conjugates were characterized using atomic force microscopy (AFM) imaging. From AFM imaging we identified that the sidewall functionalized SWNTs assisted the formation of one-dimensional close-conjugates of QDs and gold-NPs. Although the nitro- and amino-derivatives of SWNT showed weak PL, conjugation of gold-NPs to the amino-derivative quenched the PL quantitatively. On the other hand, conjugation of luminescent QDs to SWNTs resulted in a partial (similar to 35%) quenching of PL from QDs. We attributed the quenching of PL from SWNTs by gold-NPs to non-radiative energy transfer between SWNTs and gold-NPs or vice versa, and the quenching of PL from QDs is due to non-radiative energy transfer from QDs to SWNTs. In the current work, we demonstrated a simple method of close-packing of QDs and gold-NPs using functionalized SWNT templates. Also, we identified that PL properties of SWNTs and QDs are affected in the close-packed structures. SWNT and NP based hybrid materials show great promise as building blocks for nanoscale devices. In this regard the preparation and understanding of the properties of SWNT-QD and SWNT-gold-NP conjugates would be useful during the design of various hybrid nanoscale materials for device applications. (c) 2006 Elsevier B.V. All rights reserved.
• Fabrication of a quantum dot-polymer matrix by layer-by-layer conjugation

  Sayaka Ishii, Rintaro Ueji, Shunsuke Nakanishi, Yuichiro Yoshida, Hideya Nagata, Tamitake Itoh, Mitsuru Ishikawa, Vasudevanpillai Biju

  JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY 183 3 285 - 291 2006年10月 [査読有り][通常論文]
   

  A polymer-quantum dot (QD) composite matrix was fabricated by a simple layer-by-layer (LBL) covalent conjugation of cadmium selenide (CdSe) QDs to poly(dimethylsiloxane) (PDMS) films. LBL covalent conjugation was preferred in the current work for avoiding possible phase separation of QDs into microdomains when directly mixed with polymers. A PDMS film was fabricated by thermal curing of a pre-polymer mixture and was silanized using 3-mercaptopropyltrimethoxy silane (3MPS). A monolayer of Use QDs was conjugated to the polymer film through thiol coupling. By repeating the fabrication of PDMS film on the QD layer, silane coupling, and QD conjugation we have successfully prepared an optically transparent multilayer polymer-QD matrix. We selected PDMS as a host polymer considering (1) photoluminescence (PL) of QDs was not affected by PDMS, (2) simple chemical conjugation of QDs to PDMS, (3) flexible structural fabrication, and (4) optical transparency. Formation of individual layers of polymer and QDs was characterized using atomic force microscopy (AFM) imaging, and the presence of QD layers inside the PDMS matrix was identified from fluorescence imaging. Besides a simple demonstration of LBL conjugation of QDs to PDMS, the preparation of an optically transparent polymer-QD matrix where PL properties of QDs are intact would be useful during the construction of QD based optical and optoelectronic devices supported in host matrixes. (c) 2006 Elsevier B.V. All rights reserved.
• Correlated measurements of plasmon resonance Rayleigh scattering and surface-enhanced resonance Raman scattering using a dark-field microspectroscopic system

  Tamitake Itoh, Yasuo Kikkawa, Kenichi Yoshida, Kazuhiro Hashimoto, Vasudevanpillai Biju, Mitsuru Ishikawa, Yukihiro Ozaki

  JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY 183 3 322 - 328 2006年10月 [査読有り][通常論文]
   

  The current work demonstrates development of a dark-field microspectroscopic system by combining Rayleigh scattering spectroscopy and surface-enhanced resonance Raman scattering (SERRS) spectroscopy on an optical microscope. The microspectroscopic system was helpful for identifying plasmon resonance Rayleigh scattering from isolated Ag nanoaggregates and simultaneous measurements of SERRS signals from the nanoaggregates. Furthermore, the use of a microspectroscopic system for correlated measurements of plasmon resonance Rayleigh scattering and SERRS signals enabled us to establish relationships between SERRS, excitation polarization, excitation energy, and plasmon resonance energy. The relationships between SERRS, excitation polarization, excitation energy, and plasmon resonance energy allowed us not only to identify optimum excitation condition for maximum SERRS but also clarification of a mechanism underlying SERRS. Details of microspectroscopic system, measurement of plasmon resonance Rayleigh scattering and SERRS, and a mechanism of SERRS are discussed. (c) 2006 Elsevier B.V. All rights reserved.
• COLL 358-Close-packing of colloidal quantum dots: Photoluminescence properties of linear and spheroid assemblies of quantum dots

  Vasudevanpillai Biju, Tamitake Itoh, Mitsuru Ishikawa

  ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 232 2006年09月 [査読有り][通常論文]
  
• Elucidation of interaction between metal-free tetraphenylporphine and surface Ag atoms through temporal fluctuation of surface-enhanced resonance Raman scattering and background-light emission

  T Itoh, K Hashimoto, Biju, V, M Ishikawa, BR Wood, Y Ozaki

  JOURNAL OF PHYSICAL CHEMISTRY B 110 19 9579 - 9585 2006年05月 [査読有り][通常論文]
   

  We have observed simultaneously temporal fluctuation of surface-enhanced resonance Raman scattering (SERRS) and its background-light emission from single Ag nanoaggregates that were adsorbed with metal-free tetraphenylporphine (H2TPP) molecules. We found that temporally stable SERRS spectra showed clearly a SERRS band that is attributed to a stretching mode of a chemical bond between a carbon atom and a non-hydrogenated nitrogen atom (C-alpha-N). This stretching mode was not observed in regular resonance Raman spectra which are free from surface enhancement. On the other hand, we also found that temporally unstable SERRS spectra did not clearly show a C-alpha-N stretching mode in SERRS bands. Furthermore, temporally stable SERRS spectra were accompanied by temporally stable background-light emission. Kobayashi et al. [J. Phys. Chem. 1985, 89, 5174] reported that formation of an Ag-N bond between surface Ag atoms and non-hydrogenated N atoms in a pyrrole ring enhances the intensity of a C-alpha-N stretching mode. Thus, the observed relationship between clear appearance of a C-alpha-N stretching mode and temporal stability of SERRS plus background-light emission strongly suggests that formation of a stable Ag-N bond suppresses fluctuation of both SERRS and background-light emission. Furthermore, the observed relationship implies that chemical contribution to SERRS is stabilization of H2TPP molecules that are adsorbed on SERRS-active sites by formation of Ag-N bonds. Additionally, we attributed background-light emission to luminescence of complexes between H2TPP molecules and surface Ag atoms considering possible formation of Ag-N bonds, synchronized SERRS intensity with background-light emission intensity, blue-shifted background-light emission maxima from normal fluorescence maxima, and previous reports related to electronic structures of H2TPP molecules on Ag surfaces.
• Surface-enhanced resonance Raman scattering and background light emission coupled with plasmon of single Ag nanoaggregates

  T Itoh, Biju, V, M Ishikawa, Y Kikkawa, K Hashimoto, A Ikehata, Y Ozaki

  JOURNAL OF CHEMICAL PHYSICS 124 13 1347081 - 1347086 2006年04月 [査読有り][通常論文]
   

  We investigated the optical properties of isolated single aggregates of Ag nanoparticles (Ag nanoaggregates) on which rhodamine 6G molecules were adsorbed to reveal experimentally a correlation among plasmon resonance Rayleigh scattering, surface-enhanced resonance Raman scattering (SERRS), and its background light emission. From the lack of excitation-laser energy dependence of background emission maxima we concluded that the background emission is luminescence, not Raman scattering. The polarization dependence of both SERRS and background emission was the same as that of the lowest-energy plasmon resonance maxima, which is associated with a longitudinal plasmon. From the common polarization dependence, we identified that the lowest-energy plasmon is coupled with both SERRS and background emission. In addition, we revealed that the lowest-energy plasmon with a higher quality factor (Q factor) yields larger SERRS and background emission intensity. Also, we identified that the Q factor dependence of the SERRS intensity was similar to that of the background emission intensity. This similarity directly supported us to demonstrate an enhancement of both SERRS and background emission by coupling with a common plasmon radiative mode. (c) 2006 American Institute of Physics.
• Subsecond luminescence intensity fluctuations of single CdSe quantum dots

  Biju, V, Y Makita, T Nagase, Y Yamaoka, H Yokoyama, Y Baba, M Ishikawa

  JOURNAL OF PHYSICAL CHEMISTRY B 109 30 14350 - 14355 2005年08月 [査読有り][通常論文]
   

  Photoluminescence (PL) intermittency characteristics are examined for single quantum dots (QDs) in a CdSe QD sample synthesized at a slow rate at 75 degrees C. Although the PL quantum efficiency was relatively low (similar to 0.25), we noticed that the PL intensity of single CdSe QDs fluctuated on a subsecond time scale with short-lived "on" and "off' states. The subsecond PL intensity fluctuations of CdSe QDs are different from "on" and "off' PL blinking generally observed for QDs fluctuating on a millisecond to minute time scale. We characterized single QDs by identifying polarized excitations, topographic imaging using atomic force microscopy (AFM), and transmission electron microscopy (TEM). From analysis of the PL intensity trajectories from > 100 single CdSe QDs, the average intermittency time was 213 ms. From the PL quantum efficiency, slow growth of QDs, intensity trajectory analyses, and previous reports relating surface trap states and PL properties of QDs, we attribute the subsecond PL intensity fluctuations of single CdSe QDs and short-lived "on" and "off' states to a high-density distribution of homogeneous surface trap states.
• Temperature-sensitive photoluminescence of CdSe quantum dot clusters

  Biju, V, Y Makita, A Sonoda, H Yokoyama, Y Baba, M Ishikawa

  JOURNAL OF PHYSICAL CHEMISTRY B 109 29 13899 - 13905 2005年07月 [査読有り][通常論文]
   

  The formation of narrow size dispersed and nanometer size aggregates (clusters) of cadmium selenide (CdSe) quantum dots (QDs) and their temperature-sensitive photolumineseence (PL) spectral properties close to room temperature (298 K) are discussed. CdSe QDs formed stable clusters with an average diameter of similar to 27 nm in the absence of coordinating solvents. Using transmission electron microscopy (TEM) imaging, we identified the association of individual QDs with 2-5 nm diameters into clusters of uniform size. A suspension of these clusters in different solvents exhibited reversible PL intensity changes and PL spectral shifts which were correlated with temperature. Although the PL intensity of CdSe QDs encapsulated in host matrixes and the solid state showed a response to temperature under cryogenic conditions, the current work identified for the first time QD clusters showing temperature-sensitive PL intensity variations and spectral shifts at moderate temperatures above room temperature. Temperature-sensitive reversible PL changes of clusters are discussed with respect to reversible thermal trapping of electrons at inter-QD interfaces and dipole-dipole interactions in clusters. Reversible luminescence intensity variations and spectral shifts of QD clusters show the potential for developing sensors based on QD nanoscale assemblies.
• Display and retraction of outer membrane cytochromes by Shewanella oneidensis in response to electron acceptor availability

  Y Gorby, Biju, V, D Pan, J McLean, D Saffarini, J Fredrickson, HP Lu

  GEOCHIMICA ET COSMOCHIMICA ACTA 69 10 A671 - A671 2005年05月 [査読有り][通常論文]
  
• Structure and properties of narrow size-dispersed nanoclusters of quantum dots.

  VP Biju, Y Makita, H Yokoyama, Y Baba, M Ishikawa

  ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 229 U675 - U675 2005年03月 [査読有り][通常論文]
  
• Intermittent single-molecule interfacial electron transfer dynamics.

  Biju, V, M Micic, DH Hu, HP Lu

  ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 229 U790 - U790 2005年03月 [査読有り][通常論文]
  
• Novel properties of luminescent quantum dots and their application to nano-sensors

  Mitsuru Ishikawa, Vasudevan Pillai Biju

  IDW/AD '05: PROCEEDINGS OF THE 12TH INTERNATIONAL DISPLAY WORKSHOPS IN CONJUNCTION WITH ASIA DISPLAY 2005, VOLS 1 AND 2 929 - 932 2005年 [査読有り][通常論文]
   

  Photoluminescence (PL) intermittency was examined for single CdSe quantum dots (QDs) synthesized at 75 degrees C. The PL intensity of single CdSe QDs fluctuated on a subsecond time scale. The subsecond PL fluctuations, the average of which was 213 ms, are different from "on" and "off'' PL blinking generally observed for QDs fluctuating on second to minute time scale. From previous reports, we attribute the subsecond PL intensity fluctuations to a high-density distribution of homogeneous surface trap states.
• Synthesis of CdTe quantum dots using a heterogeneous process at low temperature and their optical and structural properties

  R Jose, Biju, V, Y Kamakoa, T Nagase, Y Makita, Y Shinohara, Y Baba, M Ishikawa

  APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING 79 8 1833 - 1838 2004年12月 [査読有り][通常論文]
   

  Luminescent CdTe quantum dots (QDots) have been synthesized through a low-temperature process employing a heterogeneous reaction between cadmium acetate and tri-n-octyl phosphine tellurium (TOPTe) in the presence of tri-n-octyl phosphine oxide (TOPO). UV-visible absorption spectra revealed that monodispersed CdTe QDots were synthesized at 70 degreesC for 240 min. The as-synthesized CdTe QDots exhibited photoluminescence (PL) with a narrow spectral distribution (FWHM similar to 41 nm). Highly luminescent CdTe QDots with PL quantum yield (QY) up tosimilar to 33% were size selected from the ensemble. X-ray and electron diffraction measurements revealed that CdTe crystallized in a wurtzite-type structure at 70 degreesC. High-resolution transmission electron microscopic measurements revealed that the CdTe particles were of regular spherical morphology with an average diameter of similar to 2.8 nm. The present experiment demonstrates, in addition to an advantage in green chemistry, that a low-temperature process allows an extended period of time for crystallization that is useful for synthesizing defect-free QDots with higher PL QY.
• Intermittent single-molecule interfacial electron transfer dynamics

  Biju, V, M Micic, DH Hu, HP Lu

  JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 126 30 9374 - 9381 2004年08月 [査読有り][通常論文]
   

  We report on single-molecule studies of photosensitized interfacial electron transfer (ET) processes in Coumarin 343 (C343)-TiO2 nanoparticles (NP) and Cresyl Violet (CV+)-TiO2 NP systems, using time-correlated single-photon counting coupled with scanning confocal fluorescence microscopy. Fluorescence intensity trajectories of individual dye molecules adsorbed on a semiconductor NP surface showed fluorescence fluctuations and blinking, with time constants distributed from milliseconds to seconds. The fluorescence fluctuation dynamics were found to be inhomogeneous from molecule to molecule and from time to time, showing significant static and dynamic disorders in the interfacial ET reaction dynamics. We attribute fluorescence fluctuations to the interfacial ET reaction rate fluctuations, associating redox reactivity intermittency with the fluctuations of molecule-TiO2 electronic and Franck-Condon coupling. Intermittent interfacial ET dynamics of individual molecules could be characteristic of a surface chemical reaction strongly involved with and regulated by molecule-surface interactions. The intermittent interfacial reaction dynamics that likely occur among single molecules in other interfacial and surface chemical processes can typically be observed by single-molecule studies but not by conventional ensemble-averaged experiments.
• Dynamics of photoinduced electron-transfer processes in fullerene-based dyads: Effects of varying the donor strength

  KG Thomas, Biju, V, PV Kamat, MV George, DM Guldi

  CHEMPHYSCHEM 4 12 1299 - 1307 2003年12月 [査読有り][通常論文]
   

  Two classes of fullerene-based donor-bridge-acceptor (D-B-A) systems containing donors of varying oxidation potentials have been synthesized. These systems include fullerenes linked to heteroaromatic donor groups (phenothiazine/phenoxazine) as well as substituted anilines (p-anisidine/p-toluidine). In contrast to the model compound, an efficient intramolecular electron transfer is observed from the fullerene singlet excited state in polar solvents. An increase in the rate constant and quantum yield of charge separation (k(cs) and Phi(cs)) has been observed for both classes of dyads, with decrease in the oxidation potentials of the donor groups. this observation indicates that the rates of the forward electron transfer fall in the normal region of the Marcus curve. The long-lived charge separation enabled the characterization of electron transfer products, namely, the radical cation of the donor and radical anion of the pyrrolidinofullerene, by using nanosecond transient absorption spectroscopy. The small reorganization energy (lambda) of C-60 coupled with large negative free energy changes (-DeltaGdegrees) for the back electron transfer places the back electron process in the inverted region of Marcus curve, thereby stabilizing the electron transfer products.
• Spatial heterogeneity in a polymer thin film probed by single molecules

  VP Biju, JY Ye, M Ishikawa

  JOURNAL OF PHYSICAL CHEMISTRY B 107 39 10729 - 10735 2003年10月 [査読有り][通常論文]
   

  Spatial heterogeneity in a polymer melt has been divided into two distributions that are distinguished by different relaxation behaviors of single-molecule probes near the nominal calorimetric glass-transition temperature (T-g). The fluorescence intensity and lifetime of individual molecules in a polymer film each exhibited a bimodal histogram that involved fast- and slow-relaxation sites at T-g - 8 K and T-g + 7 K, whereas a monomodal histogram composed of fast-relaxation sites was observed at T-g + 30 K. Temperature has no important effect on the center of each distribution in these histograms. Instead, occurrences of slow-relaxation sites decreased as the temperature increased from T-g - 8 K to T-g + 7 K and disappeared at T-g + 30 K. Furthermore, a change in the single-molecule fluorescence intensity was traced at fast- and slow-relaxation sites in a polymer film. At T-g - 8 K and T-g 30 K, no substantial change in fluorescence intensity was observed at each site for greater than or equal to3 h, whereas, at T-g + 7 K, the fluorescence intensity varied with an average time constant of 200-300 s at fast- and slow-relaxation sites. This variation comes most likely from a cooperative rearrangement of fast- and slow-relaxation sites, not from a migration of the single molecules between static fast- and slow-relaxation sites.
• Fluorophore modified microcontact prints: A methodology for readout using fluorescence microscopy (vol 46, pg 155, 2002)

  Biju, V, M Gad, W Mizutani, S Murata, M Ishikawa

  JOURNAL OF IMAGING SCIENCE AND TECHNOLOGY 46 4 III - III 2002年07月 [査読有り][通常論文]
  
• Fabrication of standard samples for single-molecule fluorescence imaging

  Biju, V, M Takeuchi, K Umemura, M Gad, M Ishikawa

  JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 41 3A 1579 - 1586 2002年03月 [査読有り][通常論文]
   

  A strategy for fabricating a single-molecule sample was developed to meet the requirements for a standard sample, which is characterized by uniform fluorescence intensity and uniform spatial distribution of single molecules on a glass surface. Individual chromophores of hexachlorofluorescein or Texas Red were immobilized on a glass surface by covalent bonding through molecular tethers. Fluorescence intensity and spatial distribution of individual fluorescent spots were evaluated using far-field video microscopy. Uniform fluorescence intensity was quantitatively represented by a sharp distribution in the histogram of the fluorescence photocounts. To determine the spatial distribution of fluorescent spots, uniform or not, the statistical ensemble of the number of fluorescent spots in a small area (5 x 5 and 2 x 2 mum(2)) randomly set within the full area (100 X 100 mum(2)) was collected; then, the ensemble was compared with the Poisson distribution.
• Fluorophore modified microcontact prints: A methodology for readout using fluorescence microscopy

  Biju, V, M Gad, W Mizutani, S Murata, M Ishikawa

  JOURNAL OF IMAGING SCIENCE AND TECHNOLOGY 46 2 155 - 158 2002年03月 [査読有り][通常論文]
   

  The validity of fluorescence microscopy was investigated for imaging microcontact printed (muCP) patterns prepared by chemical modification on a glass surface. Lithographic stamps were used for patterned silanization of a glass surface, followed by chemical modification with a fluorophore. The stamped patterns modified with a fluorophore on the surface were analyzed using fluorescence microscopy. The observed fluorescence patterns were confirmed by spectral measurement to be from the fluorophores bound to the silanized pattern. This method of modifying patterned surfaces using fluorophores provides a simple way of highlighting microprinting, taking advantage of chemical modification of muCP patterns.
• Clusters of bis- and tris-fullerenes

  Biju, V, PK Sudeep, KG Thomas, MV George, S Barazzouk, PV Kamat

  LANGMUIR 18 5 1831 - 1839 2002年03月 [査読有り][通常論文]
   

  Bis- and tris-fullerene derivatives [bis-(C-60) and tris-(C-60)] form suspendable clusters in mixed solvents (80% acetonitrile and 20% toluene). These clusters are optically transparent and exhibit interesting nanostructures with sizes ranging from 100 nm to 1 mum and shapes varying from elongated wires to entangled spheres. Ground- and excited-state properties of the clusters of the mono-, bis-, and tris-fullerene derivatives are compared with the corresponding properties of their monomeric forms through steady-state and time-resolved transient absorption spectroscopy. The singlet excited-state quenching of bis- and tris-fullerene derivatives by N-methylphenothiazine (NMP) occurs with rate constants of 5.5 x 10(9) and 5.3 x 10(9) M-1 s(-1), respectively. The charge separation in these clustered- fullerene derivatives is probed by monitoring the formation and decay of the C-60 radical anion and the radical cation of NMP. An increase in the number of fullerene moieties in the molecule helps in the formation of ordered duster aggregates and this has a beneficial effect in stabilizing the electron-transfer products.
• Distribution of single molecules in polymer thin films

  Biju, V, M Yamauchi, M Ishikawa

  JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY 140 3 237 - 241 2001年05月 [査読有り][通常論文]
   

  Distribution of fluorescent dye molecules in polymer thin (similar to 100nm) films was investigated using far-field single-molecule video microscopy, by varying concentrations of dye molecules mixed in the polymer. Histograms of fluorescence photocounts of individual fluorescent spots showed wide distribution, varying in the number of fluorescent spots composed of one, two, three or group of molecules. The number of the molecules present in the fluorescent spots was also ascertained by fluorescence photobleaching experiments. Photocounts associated with maxima of the histograms were found to be independent of the concentrations; however, the number of occurrences associated with mol e th;in one molecule decreased with decreasing concentration. By reducing concentration as well as by mixing dye molecules into a polymer solution, fluorescent spots grouping more than one molecule were separated considerably into fluorescent spots including a single-molecule. (C) 2001 Elsevier Science B.V. All rights reserved.
• Photoinduced electron transfer between 1,2,5-triphenylpyrrolidinofullerene cluster aggregates and electron donors

  Biju, V, S Barazzouk, KG Thomas, MV George, PV Kamat

  LANGMUIR 17 10 2930 - 2936 2001年05月 [査読有り][通常論文]
   

  Fullerene derivative 1,2,5-triphenylpyrrolidinofullerene (TPPF) forms optically transparent clusters (mean diameter of similar to 180 nm) in toluene/acetonitrile mixtures. The bimolecular rate constants for the quenching of a singlet excited state of TPPF clusters by various electron donors (substituted anilines and heteroaromatics) were found to be significantly higher than that of the corresponding monomeric analogue. The local concentration of the fullerene molecules is much higher in these clusters because the microheterogeneous environment facilitates trapping of donor molecules. Formation of long-lived electron-transfer products, following the photoexcitation of the TPPF cluster and various electron donors, was confirmed through flash photolysis studies. The TPPF cluster-donor assemblies when deposited as a thin film on a nanostructured SnO2 semiconductor film, act as a photosensitive electrode material. Light energy can be harvested using an intermolecular electron transfer between the TPPF cluster film and the corresponding electron donor in a photoelectrochemical cell. Photocurrents of up to 0.4 muA/cm(2) have been achieved in the TPPF-N-methylphenothiazine cluster system under visible light irradiation.
• Orientation-dependent electron transfer processes in fullerene-aniline dyads

  KG Thomas, Biju, V, DM Guldi, PV Kamat, MV George

  JOURNAL OF PHYSICAL CHEMISTRY A 103 50 10755 - 10763 1999年12月 [査読有り][通常論文]
   

  Newly synthesized ortho- and para-substituted fullerene-aniline dyads exhibit orientation-dependent electron transfer under photoexcitation. Minimum energy conformation based on molecular mechanics calculations yield folded conformations for ortho-substituted dyads and extended ones for the para-substituted dyads. H-1 NMR studies also provided evidence for the folding of the anilinic group in the case of ortho-substituted dyads, Through-space charge transfer processes in these dyads were investigated using steady state fluorescence and lifetime measurements. The decrease in the spatial distance between the donor and acceptor moieties of the ortho-substituted dyads facilitated an efficient electron transfer. The marked increase in the singlet excited state deactivation rate constants and quantum yields of charge separation observed in the case of the ortho-substituted dyads, in polar solvents, further support a topographically controlled electron transfer process.
• Photoinduced charge separation and stabilization in clusters of a fullerene-aniline dyad

  KG Thomas, Biju, V, DM Guldi, PV Kamat, MV George

  JOURNAL OF PHYSICAL CHEMISTRY B 103 42 8864 - 8869 1999年10月 [査読有り][通常論文]
   

  Fullerene-bridge-aniline dyad and the model fulleropyrrolidine compound form stable, optically transparent clusters in mixtures (3:1) of acetonitrile and toluene. Ground- and excited-state properties of the clusters of the dyad and the model compound are: compared with their corresponding monomeric forms. Clustering of the dyad as well as the model compound exhibits a red-shifted emission maximum (lambda(max) similar to 738 nm) compared to their monomeric forms (lambda(max) similar to 714 nm). The electron transfer from the appended electron donor moiety to the parent fullerene core in the dyad cluster is evident from the decreased (similar to 80%) fluorescence yield. The formation of fullerene radical anion (absorption maximum at 1010 nm) with a lifetime of several hundreds of microseconds was further confirmed using nanosecond laser (337 nm) flash photolysis experiments. In contrast, the dyad molecules in their monomeric form did not yield any detectable yield of C-60 radical anion following laser pulse excitation. The failure to observe any charge-transfer intermediates following laser pulse excitation, even in polar solvents such as benzonitrile or nitromethane, suggested that fast back-electron-transfer process must be operative in the monomeric dyad system. On the other hand, clustering of the fullerene-based dyads in a mixed-solvent system can provide a unique way to decrease the rate of back electron transfer, thus stabilizing the electron-transfer products.
• Photoinduced electron transfer in clusters of a fullerene-aniline dyad.

  KG Thomas, Biju, V, MV George, DM Guldi, PV Kamat

  ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 218 U317 - U317 1999年08月 [査読有り][通常論文]
  
• Photoinduced charge separation in clusters of fullerene-aniline dyads

  Biju, V, KG Thomas, MV George, D Guldi, PV Kamat

  RECENT ADVANCES IN THE CHEMISTRY AND PHYSICS OF FULLERENES AND RELATED MATERIAL, VOL 7 99 12 296 - 303 1999年 [査読有り][通常論文]
  
• Excited-state interactions in pyrrolidinofullerenes

  KG Thomas, Biju, V, MV George, DM Guldi, PV Kamat

  JOURNAL OF PHYSICAL CHEMISTRY A 102 28 5341 - 5348 1998年07月 [査読有り][通常論文]
   

  Two new pyrrolidinofullerenes, 1 and 2, have been synthesized, and their photophysical properties have been investigated. The pyrrolidinofullerene 1 has three phenyl groups attached to the 1, 2, and 5 positions of the pyrrolidine ring. The pyrrolidinofullerene 2, on the other hand, has a flexible attachment with an N-methylaniline end group and is the prototype of a fullerene-aniline dyed. Singlet and triplet excited-state properties of these two functionalized fullerene derivatives have been examined with picosecond and nanosecond laser flash photolysis. The singlet and triplet excited states of these fullerenes exhibit characteristic absorption bands in the vis-IR region of the spectrum. The functionalization of C-60 with pyrrolidine groups shift the excited-state absorption maxima to the blue. Three different quenchers, O-2, TEMPO, and ferrocene, are employed to investigate the reactivity of triplet excited states. The bimolecular quenching rate constants determined for these quenchers were in the range of 5.3 x 10(8) to 7.7 x 10(9) M-1 s(-1). The excited-state interactions of these functionalized fullerenes are compared to that of C-60.
• Studies on intramolecular photoinduced electron transfer processes in fullerene based donor-bridge-acceptor systems

  PV Kamat, D Guldi, Biju, V, KG Thomas, MV George

  RECENT ADVANCES IN THE CHEMISTRY AND PHYSICS OF FULLERENES AND RELATED MATERIALS, VOL 6 98 8 273 - 280 1998年 [査読有り][通常論文]
  
• Excited state behavior of fullero-phenylpyrrolidines

  PV Kamat, D Guldi, D Liu, KG Thomas, Biju, V, S Das, MV George

  PROCEEDINGS OF THE SYMPOSIUM ON RECENT ADVANCES IN THE CHEMISTRY AND PHYSICS OF FULLERENES AND RELATED MATERIALS, VOL 4 97 14 122 - 128 1997年 [査読有り][通常論文]
  

講演・口頭発表等

• 酸性条件下でのニワトリ卵白リゾチームの光捕捉挙動  [通常講演]

  柚山 健一, Islam Md Jahidul, Biju Vasudevan Pillai

  2018年光化学討論会 2018年09月 ポスター発表
• Crystallization of mixed chloride-bromide methylammonium lead perovskites by optical trapping at solution surface  [通常講演]

  Md Jahidul Islam, Kenichi Yuyama, Katsuaki Konishi, Biju Vasudevan Pillai

  2018年光化学討論会 2018年09月 ポスター発表
• Electron Transfer under Large Positive Gibbs Energy: Highly-excited Quantum Dots for Energy Harnessing and Photocatalysis  [招待講演]

  Biju Vasudevan Pillai

  水素社会のための第３回国際シンポジウム 2018年08月 シンポジウム・ワークショップパネル（公募）
• Photoluminescence of Semiconductor Quantum Dots: The Roles of Electron Donors/Acceptors and Incident Photon Flux  [招待講演]

  Biju Vasudevan Pillai

  NANO2018 2018年06月 口頭発表（基調）
• Extended Diffusion of Charge Carriers in Perovskite Nanocrystal Assembly  [通常講演]

  Sushant GHIMIRE, Lata CHOUHAN, Ken-ichi YUYAMA, Yuta TAKANO, Vasudevan Pillai Biju

  日本化学会第98春季年会2018 2018年03月 口頭発表（一般）
• Semiconductor Quontum Dots in Bioimagion: Progress and Challenges  [招待講演]

  Biju Vasudevan Pillai

  9th Bangalore India NANO 2017年12月 口頭発表（招待・特別）
• Semiconductore Quantum Dots for Single-molecule Detections in Living Cells: Challenges and Progress  [招待講演]

  Biju Vasudevan Pillai

  Nanobiotechnology 2017年12月 口頭発表（招待・特別）
• Semiconductor Quantum Dots in Single Molecule Detections: Prospects and challenges  [招待講演]

  Biju Vasudevan Pillai

  ICPA 2017年11月 口頭発表（招待・特別）
• Quantum Dots for Single Molecule Detections: Recent Progress and Challenges  [招待講演]

  Biju Vasudevan Pillai

  Nanoscale 2017年10月 口頭発表（招待・特別）
• Single molecule detections &Bioimaging using Semiconductor Nanocrystals.  [通常講演]

  Biju Vasudevan Pillai

  Emerging Frontiers in Chemical Science 2017 2017年09月 口頭発表（一般）
• A Few Intracellular Pathways Of Quantum Dot Bioconjugates  [招待講演]

  Biju Vasudevan Pillai

  MAF2017 2017年09月 口頭発表（招待・特別）
• A fluorescence sensor for real-time monitoring of singlet oxygen  [通常講演]

  Reiko Kohara, Biju Vasudevan Pillai

  日本化学会第97回春季年会（2017） 2017年03月 口頭発表（一般）
• Luminescent Semiconductor Nanocrystals: Challenges and Prospects  [招待講演]

  Biju Vasudevan Pillai

  International Symposium on “New Trends in Applied Chemistry" (NTAC2017) 2017年02月 口頭発表（招待・特別）
• Selective and sensitive detection of singlet oxygen using a novel fluorogenic molecular sensor  [通常講演]

  Reiko Kohara, Biju Vasudevan Pillai

  The 17th RIES-HOKUDAI INTERNATIONAL SYMPOSIUM on JU 2016年12月 ポスター発表
• Luminescent Quantum Dots in Biomaging  [招待講演]

  Biju Vasudevan Pillai

  The 17th RIES-HOKUDAI INTERNATIONAL SYMPOSIUM on JU 2016年12月 口頭発表（招待・特別）
• Blinking and Bleaching Quantum Dots in Single-molecule Detections  [招待講演]

  Biju Vasudevan Pillai

  Asian Photochemistry Conference 2016 2016年12月 口頭発表（招待・特別）
• Impeding Oxidation and Blinking in Single Semiconductor Quantum Dots  [招待講演]

  Biju Vasudevan Pillai

  Department of Applied Chemistry Seminar 2016年11月 公開講演，セミナー，チュートリアル，講習，講義等
• Fluorescence Sensing of Nanomaterials by Photosensitization Reactions  [通常講演]

  Biju Vasudevan Pillai

  Asia Nano 2016 2016年10月 ポスター発表
• Incessant and Intermittent Photoluminescence of Quantum Dots in Single Molecule Detections  [招待講演]

  Biju Vasudevan Pillai

  AsiaNANO2016 2016年10月 口頭発表（招待・特別）
• Single-molecule Detection using Quantum Dot Labels: Challenges and Prospects  [招待講演]

  Biju Vasudevan Pillai

  HOKUDAI-NCTU Joint Symposium on Nano, Photo and Bio Sciences in 2016 2016年10月 口頭発表（招待・特別）

その他活動・業績

• Lead-Free Halide Perovskite Materials and Optoelectronic Devices: Progress and Prospective

  Iago López-Fernández, Donato Valli, Chun Yun Wang, Subarna Samanta, Takuya Okamoto, Yi Teng Huang, Kun Sun, Yang Liu, Vladimir S. Chirvony, Avijit Patra, Juliette Zito, Luca De Trizio, Deepika Gaur, Hong Tao Sun, Zhiguo Xia, Xiaoming Li, Haibo Zeng, Iván Mora-Seró, Narayan Pradhan, Juan P. Martínez-Pastor, Peter Müller-Buschbaum, Vasudevanpillai Biju, Tushar Debnath, Michael Saliba, Elke Debroye, Robert L.Z. Hoye, Ivan Infante, Liberato Manna, Lakshminarayana Polavarapu Advanced Functional Materials 2023年 

  Halide perovskites, in the form of thin films and colloidal nanocrystals, have recently taken semiconductor optoelectronics research by storm, and have emerged as promising candidates for high-performance solar cells, light-emitting diodes (LEDs), lasers, photodetectors, and radiation detectors. The impressive optical and optoelectronic properties, along with the rapid increase in efficiencies of solar cells and LEDs, have greatly attracted researchers across many disciplines. However, most advances made so far in terms of preparation (colloidal nanocrystals and thin films), and the devices with highest efficiencies are based on Pb-based halide perovskites, which have raised concerns over their commercialization due to the toxicity of Pb. This has triggered the search for lower-toxicity Pb-free halide perovskites and has led to significant progress in the last few years. In this roadmap review, researchers of different expertise have joined together to summarize the latest progress, outstanding challenges, and future directions of Pb-free halide perovskite thin films and nanocrystals, regarding their synthesis, optical spectroscopy, and optoelectronic devices, to guide the researchers currently working in this area as well as those that will join the field in the future.
• 単一sp²炭素クラスターにおける物理・化学欠陥挙動のSERS分析

  伊藤民武, 山本裕子, 田丸博晴, BIJU Vasudevanpillai, 脇田慎一 プラズモニクスシンポジウム 13th 2016年
• 光化学反応による金ナノクラスターの発光特性制御

  濱田守彦, 濱田守彦, 小原怜子, 小原怜子, 中西俊介, 脇田慎一, BIJU Vasudevanpillai 光化学討論会要旨集(CD-ROM) 2015 2015年
• 単一SERSホットスポットにおけるスペクトル変化分析

  伊藤民武, 山本裕子, 田丸博晴, BIJU Vasudevanpillai, 脇田慎一 応用物理学会春季学術講演会講演予稿集(CD-ROM) 62nd 2015年
• 光化学表面改質による半導体量子ドットの明滅現象の抑制および発光強度の増強

  濱田守彦, 竹之越規史, 脇田慎一, 中西俊介, BIJU Vasudevanpillai 日本化学会講演予稿集 95th (2) 2015年
• ナノグラファイトクラスターにおける欠陥ダイナミクスのSERS分析

  伊藤民武, 山本裕子, 田丸博晴, BIJU Vasudevanpillai, 脇田慎一 応用物理学会秋季学術講演会講演予稿集(CD-ROM) 76th 2015年
• 単一銀ナノ粒子2量体間隙に吸着した色素分子のSERSスペクトル変化

  伊藤民武, 山本裕子, 山本裕子, BIJU Vasudevanpillai, 脇田慎一, 田丸博晴 光化学討論会要旨集(CD-ROM) 2015 2015年
• プラズモン共鳴による単一ラマンモードの選択的増強の観測

  伊藤民武, 山本裕子, 田丸博晴, BIJU Vasudevanpillai, 脇田慎一 応用物理学会春季学術講演会講演予稿集(CD-ROM) 61st 2014年
• 結合振動子モデルを用いた銀ナノ粒子2量体と色素分子で構成された電磁気学的強結合系の評価

  伊藤民武, 山本裕子, 田丸博晴, BIJU Vasudevanpillai, 脇田慎一, 尾崎幸洋 光化学討論会要旨集(CD-ROM) 2014 2014年
• 銀ナノ粒子2量体と色素で構成されたプラズモン-分子双極子強結合系の古典的結合振動子モデルを用いた評価

  伊藤民武, 山本裕子, 田丸博晴, BIJU Vasudevanpillai, 脇田慎一, 尾崎幸洋 応用物理学会秋季学術講演会講演予稿集(CD-ROM) 74th 2013年
• 光化学反応による量子ドットの発光強度の増強

  濱田守彦, 濱田守彦, 竹之越規史, 竹之越規史, 脇田慎一, 中西俊介, BIJU Vasudevanpillai, BIJU Vasudevanpillai 光化学討論会講演要旨集 2013 2013年
• 太陽電池特性向上に向けた光化学反応によるCdSe/ZnS量子ドット表面の不活化

  濱田守彦, 濱田守彦, 竹之越規史, 竹之越規史, 的崎圭司, FENG Qi, 脇田慎一, 中西俊介, BIJU Vasudevanpillai 応用物理・物理系学会中国四国支部合同学術講演会講演予稿集 2013 2013年
• 18pHB-4 四光波混合法を用いたCdSe/ZnS量子ドットと環状分子溶媒の動的相互作用の検出(18pHB 励起子・ポラリトン,領域5(光物性))

  廣澤 佑亮, 香西 浩嘉, 宮川 勇人, 鶴町 徳昭, 小柴 俊, 中西 俊介, Biju V. P 日本物理学会講演概要集 67 (2) 673 -673 2012年08月24日
• Blinking Suppression in Semiconductor Quantum Dots and Single-molecule Imaging

  BIJU Vasudevan Pillai 化学と工業 = Chemistry and chemical industry 64 (8) 625 -625 2011年08月01日
• 25pHB-7 コロイド状CdSe/ZnS量子ドットの位相緩和の溶媒効果(25pHB 微粒子・ナノ結晶,領域5(光物性))

  香西 浩嘉, 宮川 勇人, 鶴町 徳昭, 小柴 俊, 伊藤 寛, 中西 俊介, Biju V. P., 石川 満 日本物理学会講演概要集 66 (1) 741 -741 2011年03月03日
• 25pHB-8 CdSe/ZnS単一量子ドットにおける電子移動によるBlinking抑制(25pHB 微粒子・ナノ結晶,領域5(光物性))

  濱田 守彦, 鶴町 徳昭, 伊藤 寛, 中西 俊介, 石川 満, Biju V. 日本物理学会講演概要集 66 (1) 741 -741 2011年03月03日
• 量子ドット蛍光単一分子測定で細胞シグナル伝達初期過程の謎を解く

  石川 満, ビジュ ヴァスデヴァンピライ 高分子 60 (2) 76 -77 2011年02月01日
• Photochemical Reaction of CdSe/ZnS Single Quantum Dots with Amine

  M. Hamada, N. Tsurumachi, S. Nakanishi, E. S. Shibu, M. Ishikawa, V. Biju Proc. IQEC/CLEO Pacific Rim 2011 381 -383 2011年 [査読無し][通常論文]
  
• Effect of solvents on optical coherence properties of CdSe/ZnS quantum dots in solution detected by femtosecond four-wave mixing

  H. Kouzai, Y. Hirosawa, H. Miyagawa, N. Tsurumachi, S. Koshiba, S. Nakanishi, V. Biju, M. Ishikawa Proc. IQEC/CLEO Pacific Rim 2011 2163 -2165 2011年 [査読無し][通常論文]
  
• 24aWQ-1 コロイド状CdSe/ZnS量子ドットにおける位相緩和の溶媒効果(24aWQ 量子ドット,領域4(半導体メゾスコピック系・局在))

  香西 浩嘉, 宮川 勇人, 鶴町 徳昭, 小柴 俊, 伊藤 寛, 中西 俊介, Biju V. P., 石川 満 日本物理学会講演概要集 65 (2) 645 -645 2010年08月18日
• 21pHW-7 ナノ粒子によるCdSe/ZnS単一量子ドットのBlinkingに対する効果(21pHW 量子ドット・グラフェン,領域4(半導体,メゾスコピック系・局在))

  濱田 守彦, 鶴町 徳昭, 中西 俊介, 伊藤 寛, Biju V., 石川 満 日本物理学会講演概要集 65 (1) 720 -720 2010年03月01日
• 30aVD-3 金属微粒子との相互作用によるCdSe量子ドットの発光特性変化(30aVD 微粒子・ナノ結晶・局在中心,領域5(光物性))

  松本 祐介, 山岡 洋也, 鶴町 徳昭, 伊藤 寛, 中西 俊介, Biju V., 伊藤 民武, 石川 満 日本物理学会講演概要集 64 (1) 764 -764 2009年03月03日
• 単一酵母菌の細胞壁の表面増強ラマン散乱分光分析 : 細胞表面の単一分子分析

  伊藤 民武, スジス アチヤナチル, 安部 博子, 吉田 健一, ビジュ バステバンピライ, 石川 満 レーザー学会研究会報告 = Reports on the Topical meeting of the Laser Society of Japan 382 37 -41 2009年01月15日
• 19aZB-10 量子ドット・ポリマー系の発光特性(微粒子・ナノ結晶,表面・薄膜,領域5,光物性)

  金本 嶺泰, 石井 さやか, 松本 祐介, 菅野 恵一郎, 伊藤 寛, 鶴町 徳昭, 中西 俊介, Biju Vasudevanpillai, 伊藤 民武, 石川 満 日本物理学会講演概要集 62 (1) 711 -711 2007年02月28日
• SERSの原理とマイクロバイオイメージング応用

  伊藤 民武, BIJU Vasudevanpillai, 石川 満, 吉田 健一, 尾崎 幸洋, 福岡 隆夫 電気学会研究会資料. BMS, バイオ・マイクロシステム研究会 = The papers of Technical Meeting on Bio Micro Systems, IEE Japan 2007 (1) 13 -19 2007年01月30日
• Temperature-Sensitive Photoluminescence of CdSe Quantum Dot Clusters

  Vasudevanpillai Biju, Yoji Makita, Akinori Sonoda, Hiroshi Yokoyama, Yoshinobu Baba, Mitsuru Ishikawa J. Phys. Chem. B 109 (29) 13899 -905 2005年07月28日 [査読有り][通常論文]
   

  The formation of narrow size dispersed and nanometer size aggregates (clusters) of cadmium selenide (CdSe) quantum dots (QDs) and their temperature-sensitive photoluminescence (PL) spectral properties close to room temperature (298 K) are discussed. CdSe QDs formed stable clusters with an average diameter of approximately 27 nm in the absence of coordinating solvents. Using transmission electron microscopy (TEM) imaging, we identified the association of individual QDs with 2-5 nm diameters into clusters of uniform size. A suspension of these clusters in different solvents exhibited reversible PL intensity changes and PL spectral shifts which were correlated with temperature. Although the PL intensity of CdSe QDs encapsulated in host matrixes and the solid state showed a response to temperature under cryogenic conditions, the current work identified for the first time QD clusters showing temperature-sensitive PL intensity variations and spectral shifts at moderate temperatures above room temperature. Temperature-sensitive reversible PL changes of clusters are discussed with respect to reversible thermal trapping of electrons at inter-QD interfaces and dipole-dipole interactions in clusters. Reversible luminescence intensity variations and spectral shifts of QD clusters show the potential for developing sensors based on QD nanoscale assemblies.
• 量子ドットクラスターの温度に依存する発光特性

  石川満, BIJU V. P., 槙田洋二, 苑田晃成, 横山浩, 馬場嘉信, 馬場嘉信 光化学討論会講演要旨集 2005 2005年
• 蛍光性半導体量子ドットの低温合成法

  石川満, BIJU V P, JOSE R, 長瀬智美, 槙田洋二, 篠原康雄, 馬場嘉信 光化学討論会講演要旨集 2004 2004年
• 単一分子運搬のためのマイクロチャネル内における蛍光ナノ粒子拡散係数測定

  山岡禎久, DANG F, BIJU V P, 西本尚弘, 中西博昭, 篠原康雄, 石川満, 馬場嘉信 化学とマイクロ・ナノシステム研究会講演要旨集 10th 2004年

受賞

• 2023年09月 The Japanese Photochemistry Association The Japanese Photochemistry Association Award
  

共同研究・競争的資金等の研究課題

• ナノ共振器－プラズモン強結合を用いた高効率光反応システムの開拓とその学理解明

  日本学術振興会：科学研究費助成事業 特別推進研究

  研究期間 : 2018年04月 -2023年03月 

  代表者 : 三澤 弘明, 笹木 敬司, 上野 貢生, Biju V・Pillai, 村越 敬

   

  電磁場シミュレーションにより、本モード強結合とアンサンブル強結合との差異に関する理解を深めた。その中で、金ナノディスクの密度が比較的低い状態においては、結合強度がアンサンブル強結合と同様ディスク数の1/2乗に比例して増強されることを確認したが、数密度が増大して金ナノディスク間距離が近接すると近接場相互作用により、結合強度がアンサンブル強結合に比べて増強することを明らかにし、実験的にもそれを確認した。 また、金ナノディスクの数密度が低い状態において吸収スペクトル、および近接場スペクトルが飽和する現象を解明するため、単一金ナノディスクをナノ共振器に結合させた状態をシミュレーションし、その分裂エネルギーから得られる空間のサイズを求めた。その結果、別途求めた金ナノディスクの消光断面積などと比較して一桁程度大きな値が得られ、この空間に存在する金ナノディスクが共振器と空間的にコヒーレントに結合するコヒーレンスエリアとなっていると推論している。さらに、フェムト秒過渡吸収測定から結合強度を増強させると、非強結合電極では見られない金から酸化チタンへの電子注入が増強されることを実験的に検証した。 また、金－銀合金ナノ粒子を用いてナノ共振器と結合させたところ結合強度が金の場合に比べて2倍程度増強し、「超強結合」となることを明らかにした。さらに、本超強結合電極を用いて水を電子源とする光電流を測定したところ、金と比べて2倍程度増強されること、またフェムト秒過渡吸収より金から酸化チタンへの電子注入が増強していることを明らかにした。 さらに、強結合電極の最適化を図るため、水の酸化反応の助触媒としてコバルト酸化物を金ナノ粒子の近傍に空間選択的に形成させ、反応効率を2倍以上増強することに成功した。また、キノコ型の金ナノ粒子を用いて近接場の空間制御を行い、反応効率を30%増強することにも成功した。
• Defect-free, Highly-luminescent and Non-blinking Perovskite Nanocrystals

  日本学術振興会：科学研究費助成事業 基盤研究(B)

  研究期間 : 2019年04月 -2023年03月 

  代表者 : Biju V・Pillai

   

  The research focused on defect passivation of lead halide perovskite nanocrystals (PNCs), quantum dots (PQDs), and microcrystals (PMCs), to develop defect-free LHPs. In this project, cesium (Cs)-, formamidinium (FA)-, and methylammonium (MA) lead bromide and iodide PNCs, PQDs, and PMCs with the visible-to-near infrared emission were synthesized by solution processing (colloidal synthesis), laser trapping (spatiotemporally controlled synthesis), or inverse temperature crystallization. The as-synthesized PNCs, PQDs, and PMCs showed short photoluminescence (PL) lifetimes, low PL intensities, and intense PL blinking. These poor characteristics are attributed mainly to ionic defects, forming deep traps in the bandgap and promoting nonradiative exciton recombination. Thus, this research focussed on the halide defect filling in PNCs, PQDs, and PMCs. Halide defect filling was carried out in single PNCs, single PQDs, and single PMCs by observing the PL lifetime, PL intensity, and PL blinking in real-time. The defect filling in single PNCs and PQDs provided PL quantum efficiency as high as 96% with near-complete blinking suppression. The defect filling in PMCs increased the PL lifetime and intensity, which further helped engineer the bandgap in perovskites. Thus, this research progressed to the realization of defect filling in halide perovskites and achievement of perovskite NCs, PQDs, and PMCs with longer PL lifetimes and higher PL intensities, or better quantum efficiencies than the as-synthesized halide perovskites.
• One and multiple photon induced generation and stabilization of multi-excitons in quantum dot superlattices

  文科省：新学術領域研究 研究領域提案型

  研究期間 : 2017年04月 -2019年03月 

  代表者 : Biju Vasudevan Pillai

   

  This project accomplished two key goals: (1) controlled the photoluminescence blinking of quantum dots (CdSe-ZnS QDs) by the scavenging of deep holes generated in highly-excited QDs, which was by electron transfer beyond the limitations of Marcus Theory, and (2) generated and stablished multiple charge carriers in lead halide perovskite nanocrystals (PNCs), which was by the preparation of superlattices of PNCs. The above two results became possible by controlling the numbers of excitation photons, excitons generated and photoactivated nanocrystals. Blinking suppression in a QD and stabilization of charge carriers in PNC superlattices were accomplished by exceeding the conventional 1 photon: 1 exciton: 1 chromophore relation. The above results were beyond the proposed goals, demonstrating (i) real-time blinking suppression in CdSe-ZnS QDs exposed to N,N-dimethylaniline (DMA), which was by electron transfer under a large positive Gibbs (free) energy change (ACS Nano 2018, 12, 9060) -beyond the expectations of Marcus theory. Furthermore, the blinking suppression was helpful for understanding and overcoming oxidation of PNCs (Angew. Chem. Int. Ed. 2019, 58, 4875). Also, this project accomplished optically-controlled amplified emission from PNC superlattices. Interestingly, under low-intensity excitation, a PNC superlattice showed unusually delayed emission (Angew. Chem. Int. Ed. 2017, 56, 1214), which became extremely fast and spatially confined at higher excitation intensities (ACS Energy Lett. 2018, 4, 133).
• Efficient utilization of the excitation energy of highly-excited quantum dots for photoreactions

  文科省：新学術領域研究 研究領域提案型

  研究期間 : 2015年04月 -2017年03月 

  代表者 : Biju Vasudevan Pillai

   

  Aim of this project was to develop methods for efficient utilization of the energy of highly-excited nanoparticles (NPs) such as quantum dots (QDs) and perovskite nanocrystals (PNCs). Highly-excited NPs were generated by high-intensity laser irradiation. However, energy of such NPs is lost by ultrafast radiative and non-radiative recombination of photo-generated charge carriers. Therefore, extraction of absorbed energy towards practical applications is an important challenge. Here we developed photochemical and photophysical methods for extracting the energy of such NPs. At first, a part of the energy absorbed by QDs was extracted by activation of oxygen into singlet oxygen, which was followed by using singlet oxygen as the secondary energy source for chemical reactions. Here, we developed and used two novel singlet oxygen scavengers. Next, we applied highly-excited QDs to DNA molecules, which resulted in electron transfer from DNA to ionized QDs and formation of QD-DNA conjugates. Finally, we investigated stability of photo-generated charge carriers in highly-excited PNCs by preparation of self-assembled PNC structures. When compared with a PNC isolated in a solution, prolonged stability for photo-generated charge carriers was found for self-assembled structures, which is attributed to trapping or hopping of electrons and holes in or among PNCs. Successively, charge carriers in such PNCs were efficiently extracted by employing electron acceptors such as fullerene, which opens a method for efficient utilization of photoactivated PNCs for solar energy harvesting.
• 二量化、クラスタ構成、および膜受容体細胞内輸送に関する単一分子蛍光の研究

  日本学術振興会：科学研究費助成事業 若手研究(B)

  研究期間 : 2012年04月 -2015年03月 

  代表者 : BIJU V・Pillai

   

  本研究は、個々の細胞内での単一分子の時間ゲートおよび輝度ゲート蛍光イメージングに応じたEGFRの二量体化とクラスタリングの動態を調べた。初期段階ではEGF-EGFR-EGFR（ヘテロダイマー）とシグナル伝達二量体(EGF-EGFR)2が細胞内で均一に存在した。時間経過とともにシグナル伝達二量体が支配した、それはヘテロダイマーを犠牲にしてシグナル伝達二量体が形成されたことを示唆する。また、EGFRの小クラスタが約15分で出現し、細胞内取り込み前に数、量ともに増加した。結果、EGFRによる無制御シグナル伝達は、シグナル伝達二量体にヘテロダイマーの不均化抑制をすることにより抑制可能になる。
• 光分解性バイモーダルナノパーティクルの開発と、がんの可視化と治療への応用

  国立研究開発法人 科学技術振興機構 さきがけ：

  研究期間 : 2010年10月 -2014年03月
• 細胞機能を可視化する新奇な超分子ナノ材料の光創製

  日本学術振興会：科学研究費助成事業 特別研究員奨励費

  研究期間 : 2011年 -2013年 

  代表者 : BIJU Vasudevan Pillai, BIJU VasudevanPillai, SHIBU Edakkattuparambil, EDAKKATTUPARAMBIL Shibu

   

  Our aim of this proposal is to develop a novel low-toxic, chemically stable, and highly-luminescent nanoparticles for single-molecule bio-sensing and -imaging using light as a resourceful tool. In this project, two types of novel fluorescent nanomaterials are prepared, which are fullerene-shelled CdSe-ZnS quantum dots and gold quantum clusters (Au25). Here, fullerene-shelled quantum dots are prepared by a photochemical method ; whereas, the quantum clusters are prepared by the alkaline reduction of gold ions within the pockets of bovine serum albumin. At first, a fullerene thiol molecule was synthesized by multi-step thermal chemical route. Subsequently, a monolayer of fullerene is prepared on the surface of QD by the tethering of the fullerene thiol to the ZnS surface through the S-S bonding. Finally, the fullerene thiol monolayer-protected QDs were immersed in excess fullerene thiol and photoactivated. We found the formation stable and thick fullerene shells on the surface of QDs, which is due to the 2+2 photocycloaddition reaction. Further, we characterized their photoluminescence properties at ensemble and single-molecule levels. The most interesting property of the fullerene-shelled QD is its ability to show suppressed blinking. While fullerene-shelled quantum dots show blinking suppression that is suitable for single-molecule bioimaging and solar energy harvesting ; bioconjugates of Au25 efficiently entered human cells and enabled us for obtaining NIR fluorescence images of live cells. The two types of fluorescent nanomaterials enabled us for establishing collaborations with four research groups in Japan. A part of this research is published in ACS Nano 6, 1601-1608, 2012.
• 発光性半導体ナノ結晶の点滅現象制御に関する研究

  日本学術振興会：科学研究費助成事業 特定領域研究

  研究期間 : 2005年 -2006年 

  代表者 : 石川 満, BIJU Vasudevan Pillai

   

  孤立した1個の発光性量子ドットは、本質的に備えている断続的な発光の点滅現象を示すことが知られている。これは望ましくない特性なので、非点滅性の量子ドットは、時間に依存する生物的動的過程を連続的に研究する目的では要求が高い特性のひとつである。我々は単一量子ドットの点滅現象の制御に興味があり、量子ドット合成の反応温度や溶媒の種類と組成をパラメータとし、またカーボンナノチューブ、ポリマー、および金属あるいは半導体のナノ粒子を用いて、量子ドット表面を修飾した。本研究の重要な目的のひとつは、点滅を完全に抑制することである。表面の修飾により、量子ドットの発光特性が強く影響されること、そして、しばしば強く消光を起こすことを見出した。現時点で、CdSe量子ドットについて点滅の完全な抑制を達成していないものの、反応条件の制御および表面の装飾によって、下記のような重要な知見を得た。 白色発光を示すCdSe量子ドットが有機金属化合物のコロイド成長反応を用いて室温(23℃)で合成された。これらの量子ドットは粒径分布が均一にもかかわらず、発光スペクトルの半値幅が150nmと広いことが特異的である。再現性の高い発光量子収率として0.4が得られた。さらに、mercaptosuccinic酸を用いて、この量子ドットの表面を修飾して可水溶化することも可能であった。 量子ドットを用いたナノデバイスの開発では、種々の光および電子材料に量子ドットを制御して共役化させることが必要である。このような観点から、量子ドットを規則的に配置するための方法および量子ドットと共役化させた分子アセンブリの特性を評価することは重要である。本研究では、側壁を官能基で修飾した単層カーボンナノチューブにCdSe-ZnS量子ドットを共役化させ、それが量子ドットの発光特性に及ぼす影響を調べた。

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