Researcher Database

Hiroshi Uji-i
Research Institute for Electronic Science Photonics and Optical Science

Researcher Profile and Settings


  • Research Institute for Electronic Science Photonics and Optical Science

Job Title

  • Professor


  • PhD


J-Global ID

Research Interests

  • Drug Delivery System   single cell spectroscopy   Plasmonics   single molecule spectroscopy   

Research Areas

  • Nanotechnology/Materials / Optical engineering and photonics
  • Nanotechnology/Materials / Nanobioscience

Academic & Professional Experience

  • 2015/07 - Today Hokkaido University Research Institute for Electronic Science Full professor
  • 2011/10 - Today KU Leuven Department of Chemistry Research professor
  • 2004/09 - 2011/09 KULeuven Department of Chemistry Senior post-doctoral researcher for Center of Excellence
  • 2002/09 - 2004/08 KU Leuven Department of Chemistry post-doctoral research fellow


  • 1999/04 - 2002/03  Tohoku University  Graduate School of Science  Chemistry
  • 1997/04 - 1999/03  Osaka University  Graduate School of Engineering  Applied physics
  • 1993/04 - 1997/03  Osaka University  School of Engineering  Applied physics

Research Activities

Published Papers

  • Kenji Hirai, James A Hutchison, Hiroshi Uji-i
    ChemPlusChem 2192-6506 2020/08/03 [Refereed][Not invited]
  • Qiang Zhang, Han Wen, Kiri Watanabe, Ibuki Kotani, Monica Ricci, Beatrice Fortuni, Anh Thi Ngoc Dao, Akito Masuhara, Kenji Hirai, Hitoshi Kasai, Tomoko Inose, Hiroshi Uji-i
    ACS Applied Nano Materials 2574-0970 2020/07/09 [Refereed][Not invited]
  • Masaki Takeda, Masaaki Yokoyama, Kazuki Umemoto, Bozhang Lyu, Yoshihito Takahashi, Sasiphapa Rodbuntum, Junya Enomoto, Keitaro Tozawa, Tomohiro Nohara, Keisuke Tabata, Ryota Sato, Takayuki Chiba, Satoshi Asakura, Hiroshi Uji-i, Akito Masuhara
    JAPANESE JOURNAL OF APPLIED PHYSICS 59 0021-4922 2020/06 [Refereed][Not invited]
    Highly luminescent CH3NH3PbBr3 perovskite nanocrystals (PeNCs) with a high photoluminescence quantum yield value of 80% are prepared by a forced thin film reactor for continuous production. In this system, the rotating and stationary disks form a confined micro space which demonstrates a unique mixing process through continuous injection of solvents. We found that the unique mixing system leads to colloidal PeNCs with 4 nm-10 nm, which are much smaller than those of a representative T-junction system (15 nm-65 nm). It suggests that a confined micro space is effective for the capping of n-octylamine to the surface of PeNCs, resulting in suppression of the aggregation of the PeNCs and crystal growth. Also, with increasing flow velocity, the optical properties show almost no fluctuation. This system is a promising continuous system to prepare colloidal PeNCs, and can provide a synthetic protocol to be applied for light-emitting diodes as well as various other optoelectronic devices. (C) 2020 The Japan Society of Applied Physics.
  • Shuichi Toyouchi, Mathias Wolf, Yusuke Nakao, Yasuhiko Fujita, Tomoko Inose, Beatrice Fortuni, Kenji Hirai, Johan Hofkens, Steven De Feyter, James Hutchison, Hiroshi uji-i
    Nano Letters 20 2460 - 2467 1530-6992 2020/03/10 [Refereed][Not invited]
  • Yuki Tezuka, Kazuki Umemoto, Masaki Takeda, Yoshihito Takahashi, Hinako Ebe, Junya Enomoto, Sasiphapa Rodbuntum, Tomohiro Nohara, Daniela Fontecha, Satoshi Asakura, Takayuki Chiba, Madalina Ioana Furis, Tsukasa Yoshida, Hiroshi Uji-i, Akito Masuhara
    JAPANESE JOURNAL OF APPLIED PHYSICS 59 SDDC04-1 - SDDC04-5 0021-4922 2020/03 [Refereed][Not invited]
    Organic-inorganic hybrid lead halide perovskite nanocrystals (PeNCs) have received great attention as a light source for perovskite LEDs (PeLEDs) owing to the superior optical properties. However, PeNCs typically use octylamine (OAm) as capping ligands which have insulating properties. Exploring a desirable short alkylamine instead of OAm is required for the improvement of PeLEDs. Here, as one of the strategies to solve this issue, the effects of alkylamine chain length for optical properties of PeNCs and PeLED characteristics are investigated. Pentylamine is an optimal short alkylamine and precipitate luminescent PeNCs with high PLQY values of 90%. Importantly, pentylamine maintains a relatively high PLQY of 48% after spin-coating, due to the durability pentylamine has to ethyl acetate as a washing solvent. PeNCs capped with pentylamine also demonstrate an external quantum efficiency of over 1% with luminance of over 2000 cd cm(-2), indicating that pentylamine has the potential to overcome the insulator properties of PeNC thin film. (C) 2019 The Japan Society of Applied Physics
  • Kenji Hirai, Rie Takeda, James A Hutchison, Hiroshi Uji-I
    Angewandte Chemie (International ed. in English) 59 5332 - 5335 2020/01/22 [Refereed][Not invited]
    Light-molecule strong coupling has emerged within the last decade as an entirely new method to control chemical reactions. A few years ago it was discovered that the chemical reactivity could be altered by vibrational strong coupling (VSC). While the potential of VSC in organic chemistry appears enormous, only a limited number of reactions have been investigated under VSC to date, including solvolysis and deprotection reactions. Here we investigate the effect of VSC on a series of aldehydes and ketones undergoing Prins cyclization, an important synthetic step in pharmaceutical chemistry. We observe a decrease of the second-order rate constant with VSC of the reactant carbonyl stretching groups. We measure an increased activation energy due to VSC, but proportional changes in activation enthalpy and entropy suggest no substantive change in reaction pathway. The addition of common cycloaddition reactions to the stable of VSC-modified chemical reactions is another step towards establishing VSC as a genuine tool for synthetic chemistry.
  • Kenji Hirai, Taisei Kitagawa, Hideki Fujiwara, Jenny Pirillo, Yuh Hijikata, Tomoko Inose, Hiroshi Uji-i
    Chemical Communications 56 (67) 9651 - 9654 1359-7345 2020 [Refereed][Not invited]

    A fluorophore encapsulated in a metal–organic framework showed photochromic multicolour fluorescence.

  • Hans Van Gorp, Peter Walke, Joan Teyssandier, Brandon E. Hirsch, Hiroshi Uji-i, Kazukuni Tahara, Yoshito Tobe, Mark Van der Auweraer, Steven De Feyter
    JOURNAL OF PHYSICAL CHEMISTRY C 124 (3) 1980 - 1990 1932-7447 2020/01 [Refereed][Not invited]
    The covalent functionalization of carbon-based materials through aryldiazonium chemistry has emerged as a powerful tool for physicochemical property modification. However, the characterization techniques traditionally used to assess the stability of any modification, such as thermogravimetric analysis (TGA), do not allow covalent detachment to be discriminated from the loss of physisorbed material. Here, we present a general method to differentiate these two processes by combining scanning probe microscopy with Raman spectroscopy. Using covalently modified highly oriented pyrolytic graphite (HOPG), we show that the thermally induced covalent bond breaking between the aryl groups and the HOPG surface can be directly monitored through this combined approach. Moreover, temperature-dependent Raman spectroscopy allows the kinetics of this bond breaking to be studied. Desorption activation energies can thus be initially estimated for aryl groups bearing different substituents. Finally, we highlight that the pristine HOPG structure can be restored at a relatively low temperature, opening the way for reversible covalent modification. Our results alight on a general methodology for the full characterization of covalently modified carbon materials.
  • Inose T, Toyouchi S, Lu G, Umemoto K, Tezuka Y, Lyu B, Masuhara A, Fron E, Fujita Y, Hirai K, Uji-I H
    Chemical communications (Cambridge, England) 55 (77) 11630 - 11633 1359-7345 2019/09 [Refereed][Not invited]
  • Polymeric Engineering of Nanoparticles for Highly Efficient Multifunctional Drug Delivery Systems
    B. Fortuni, T. Inose, M. Ricci, Y. Fujita, I. van Zundert, A. Masuhara, E. Fron, H. Mizuno, L. Latterini, S. Rocha, H. Uji-i
    Scientific Reports 9 2019/01 [Refereed][Not invited]
  • Kazuki Umemoto, Masaki Takeda, Yuki Tezuka, Takayuki Chiba, Matthew Schuette White, Tomoko Inose, Tsukasa Yoshida, Satoshi Asakura, Shuichi Toyouchi, Hiroshi Uji-i, Akito Masuhara
    CRYSTENGCOMM 20 (44) 7053 - 7057 1466-8033 2018/11 [Not refereed][Not invited]
    Separation of mono-dispersed CH3NH3PbBr3 perovskite quantum dots (PeQDs) using the Ostwald ripening process during aging of the perovskite nanocrystals (PeNCs) in a colloidal solution is proposed for color-tunable PeQD synthesis. Monodispersed PeNCs with size ranging from 5 to 17 nm with a spherical or square shape have been successfully prepared. Photo-luminescence spectroscopy revealed the quantum confinement effect on the spherical small QDs.
  • Hiroshi Uji-i
    The Journal of Physical Chemistry Letters 9 7117 - 7122 2018/11 [Refereed][Not invited]
  • Peter Walke, Yasuhiko Fujita, Wannes Peeters, Shuichi Toyouchi, Wout Frederickx, Steven De Feyter, Hiroshi Uji-I
    Nanoscale 10 (16) 7556 - 7565 2040-3372 2018/04/28 [Refereed][Not invited]
    Tip-enhanced Raman scattering (TERS) microscopy is a unique analytical tool to provide complementary chemical and topographic information of surfaces with nanometric resolution. However, difficulties in reliably producing the necessary metallized scanning probe tips has limited its widespread utilisation, particularly in the case of cantilever-based atomic force microscopy. Attempts to alleviate tip related issues using colloidal or bottom-up engineered tips have so far not reported consistent probes for both Raman and topographic imaging. Here we demonstrate the reproducible fabrication of cantilever-based high-performance TERS probes for both topographic and Raman measurements, based on an approach that utilises noble metal nanowires as the active TERS probe. The tips show 10 times higher TERS contrasts than the most typically used electrochemically-etched tips, and show a reproducibility for TERS greater than 90%, far greater than found with standard methods. We show that TERS can be performed in tapping as well as contact AFM mode, with optical resolutions around or below 15 nm, and with a maximum resolution achieved in tapping-mode of 6 nm. Our work illustrates that superior TERS probes can be produced in a fast and cost-effective manner using simple wet-chemistry methods, leading to reliable and reproducible high-resolution and high-sensitivity TERS, and thus renders the technique applicable for a broad community.
  • Wout Frederickx, Susana Rocha, Yasuhiko Fujita, Koen Kennes, Herlinde De Keersmaecker, Steven De Feyter, Hiroshi Uji-I, Willem Vanderlinden
    ACS Nano 12 (1) 168 - 177 1936-086X 2018/01/23 [Refereed][Not invited]
    Correlative imaging by fluorescence and force microscopy is an emerging technology to acquire orthogonal information at the nanoscale. Whereas atomic force microscopy excels at resolving the envelope structure of nanoscale specimens, fluorescence microscopy can detect specific molecular labels, which enables the unambiguous recognition of molecules in a complex assembly. Whereas correlative imaging at the micrometer scale has been established, it remains challenging to push the technology to the single-molecule level. Here, we used an integrated setup to systematically evaluate the factors that influence the quality of correlative fluorescence and force microscopy. Optimized data processing to ensure accurate drift correction and high localization precision results in image registration accuracies of ∼25 nm on organic fluorophores, which represents a 2-fold improvement over the state of the art in correlative fluorescence and force microscopy. Furthermore, we could extend the Atto532 fluorophore bleaching time ∼2-fold, by chemical modification of the supporting mica surface. In turn, this enables probing the composition of macromolecular complexes by stepwise photobleaching with high confidence. We demonstrate the performance of our method by resolving the stoichiometry of molecular subpopulations in a heterogeneous EcoRV-DNA nucleoprotein ensemble.
  • Rebeca Sola-Llano, Yasuhiko Fujita, Luis Gómez-Hortigüela, Almudena Alfayate, Hiroshi Uji-I, Eduard Fron, Shuichi Toyouchi, Joaquín Pérez-Pariente, Iñigo López-Arbeloa, Virginia Martínez-Martínez
    ACS Photonics 5 (1) 151 - 157 2330-4022 2018/01/17 [Refereed][Not invited]
    A cyanine dye (PIC) was occluded into two 1D-nanopoporus Mg-containing aluminophosphates with different pore size (MgAPO-5 and MgAPO-36 with AFI and ATS zeolitic structure types, with cylindrical channels of 7.3 Å diameter and elliptical channels of 6.7 Å × 7.5 Å, respectively) by crystallization inclusion method. Different J-aggregates are photophysically characterized as a consequence of the different pore size of the MgAPO frameworks, with emission bands at 565 nm and at 610 nm in MgAPO-5 and MgAPO-36, respectively. Computational results indicate a more linear geometry of the J-aggregates inside the nanochannels of the MgAPO-36 sample than those in MgAPO-5, which is as a consequence of the more constrained environment in the former. For the same reason, the fluorescence of the PIC monomers at 550 nm is also activated within the MgAPO-36 channels. Owing to the strategic distribution of the fluorescent PIC species in MgAPO-36 crystals (monomers at one edge and J-aggregates with intriguing emission properties at the other edge) an efficient and one-directional antenna system is obtained. The unidirectional energy transfer process from monomers to J-aggregates is demonstrated by remote excitation experiments along tens of microns of distance.
  • Kazuki Umemoto, Yong-Jin Pu, Cigdem Yumusak, Markus Clark Scharber, Matthew Schuette White, Niyazi Serdar Sariciftci, Tsukasa Yoshida, Jun Matsui, Hiroshi Uji-i, Akito Masuhara
    Microsystem Technologies 24 (1) 619 - 623 0946-7076 2018/01/01 [Refereed][Not invited]
    Cuboid fine crystals of methylammonium lead tribromide (MAPbBr3) perovskite have been synthesized by ligand-free reprecipitation method employing N,N-dimethylformamide (DMF) and 1,2,4-trichlorobenzene (TCB) as good and poor solvents, respectively. A small amount of DMF solution dissolving precursor chemicals of MAPbBr3 was rapidly injected to TCB under vigorous stirring to promote the reprecipitation. Mean crystal size could be varied between 70 and 600 nm by controlled addition of cyclohexane to TCB, since cyclohexane has been found to play a role to retard droplet diffusion. Cyclohexane was miscible with TCB but poorly miscible with DMF. Thus, addition of cyclohexane to TCB retarded diffusion of the injected droplets of DMF solution for reprecipitation of MAPbBr3. As the mixing of good and poor solvents was retarded, the recrystallization process was also slowed down, resulted in a small number of nuclei and their growth to large size. Moreover, extreme addition of cyclohexane has resulted in a hollow core spherical particles of MAPbBr3 due to aggregation of the cuboid fine crystals at the boundary between the added droplet and the poor solvent, so that the spheres formed preserving the shape of the droplet. Due to the limited miscibility of cyclohexane to DMF, increasing the cyclohexane content resulted in reduced rate of diffusion of the injected MAPbBr3 solution, thus increasing the size of the crystals.
  • Shuichi Toyouchi, Mathias Wolf, Yasuhiko Fujita, Hiroshi Uji-I
    Proceedings of SPIE - The International Society for Optical Engineering 10712 1996-756X 2018 [Refereed][Not invited]
    We have experimentally demonstrated remote plasmonic optical trapping on a chemically-synthesized silver nanowire (AgNW) induced by nonlinear optical effects, i.e. sum-frequency generation (SFG) and four wave-mixing (FWM). AgNWs were spin coated on a clean cover slip, and then covered with quantum dot (QD) aqueous solution. Two femtosecond IR laser pulses having different energies were focused on one end of the AgNW. SFG and FWM signal was observed at not only the excitation spot but also another end of AgNW through launching propagating plasmon modes. As results, it was found that QDs were trapped on the AgNW when two pulses were overlapped in time. QD resonance wavelength dependence on the trapping behavior indicates that trapping site on AgNW can be controlled.
  • Somia Rahmoun, Fabrice Mairesse, Hiroshi Uji-i, Johan Hofkens, Tadeusz Sliwa
    SIGNAL IMAGE AND VIDEO PROCESSING 11 (8) 1469 - 1476 1863-1703 2017/11 [Refereed][Not invited]
    Even though polymer chains are well studied, the convolution and diffraction effect of microscopes may cause the quality of the images to be blurry and/or noisy. This paper aims to present an automatic method to extract the curve representing a polymer chain. This curve is useful for chemical studies; for instance, the length of a polymer chain and its curvature are related to its chemical properties. A movement of the polymer chain may lead to complex geometries with possible intersections. In response to this, we developed an approach computing a piecewise curve traversing the shape. This technique relies on computing several geodesics by browsing distinct parts of the shape. Fusing these elements together allows the entire shape to be represented. The curve orientation is already preserved by considering the fusion as a graph traversal problem. The method provides promising results, validated by experts and approved by simulation.
  • B. Fortuni, T. Inose, S. Uezono, S. Toyouchi, K. Umemoto, S. Sekine, Y. Fujita, M. Ricci, G. Lu, A. Masuhara, J. A. Hutchison, L. Latterini, H. Uji-i
    CHEMICAL COMMUNICATIONS 53 (82) 11298 - 11301 1359-7345 2017/10 [Refereed][Not invited]
    A simple and fast one-step fabrication method of silver nanoparticles (AgNPs) on a polydimethylsiloxane (PDMS) film and their improvement as highly sensitive surface enhanced Raman scattering (SERS) substrates via atomically thin Au coatings is demonstrated. The thin Au layer provides oxidation resistivity while maintaining the broad spectral range SERS sensitivity of Ag nanoparticles.
  • Y. Fujita, R. Aubert, P. Walke, H. Yuan, B. Kenens, T. Inose, C. Steuwe, S. Toyouchi, B. Fortuni, M. Chamtouri, K. P. F. Janssen, S. De Feyter, M. B. J. Roeffaers, H. Uji-i
    NANOSCALE 9 (35) 13025 - 13033 2040-3364 2017/09 [Refereed][Not invited]
    A highly reproducible and controllable deposition procedure for gold nanostructures on a titanium dioxide (TiO2) surface using femtosecond laser light has been demonstrated. This is realized by precisely focusing onto the TiO2 surface in the presence of a pure gold ion solution. The deposition is demonstrated both in dot arrays and line structures. Thanks to the multi-photon excitation, we observe that the deposition area of the nanostructures can be confined to a degree far greater than the diffraction limited focal spot. Finally, we demonstrate that catalytic activity with visible light irradiation is enhanced, proving the applicability of our new deposition technique to the catalytic field.
  • Maha Chamtouri, Bart Kenens, Remko Aubert, Gang Lu, Tomoko Inose, Yasuhiko Fujita, Akito Masuhara, Johan Hofkens, Hiroshi Uji-I
    ACS Omega 2 (7) 4032 - 4038 2470-1343 2017/07/31 [Refereed][Not invited]
    Owing to their fundamental importance and practical applications, anatase TiO2 crystals with well-defined {001} and {101} facets attracted intensive research interests. In this study, we systematically investigated solvent dependence of the photoreaction of the different coexposed crystal facets during noble metal photodeposition. By examining the deposition position in each solvent, we revealed that solvents play a pivotal role on the facet selectivity. On the basis of density functional theory calculations, the solvent molecules were found to modify both the crystal facet electronic structure and the {001}-{001} heterojunction. These modifications are not only the origin of diverse charge-carrier pathways but are also responsible for carrier accumulation at specific facets that increase their reductive power. These findings are vital for a better understanding of photocatalytic materials and an improved design for the next-generation materials.
  • Gang Lu, Haifeng Yuan, Liang Su, Bart Kenens, Yasuhiko Fujita, Maha Chamtouri, Maria Pszona, Eduard Fron, Jacek Waluk, Johan Hofkens, Hiroshi Uji-i
    JOURNAL OF PHYSICAL CHEMISTRY LETTERS 8 (13) 2774 - 2779 1948-7185 2017/07 [Refereed][Not invited]
    We reveal nanoscale morphological changes on the surface of a silver nanowire (AgNW) in the conventional surface-enhanced Raman scattering (SERS) measurement condition. The surface morphology changes are due to the surface plasmon-mediated photochemical etching of silver in the presence of certain Raman probes, resulting in a dramatic increase of Raman scattering intensity. This observation indicates that the measured SERS enhancement does not always originate from the as-designed/fabricated structures themselves, but sometimes with contribution from the morphological changes by plasmon-mediated photochemical reactions. Our work provides a guideline for more reliable SERS measurements and demonstrates a novel method for simple and site specific engineering of SERS substrate and AgNW probes for designing and fabricating new SERS systems, stable and efficient TEAS mapping, and single-cell SERS endoscopy.
  • B. Fortuni, Y. Fujita, M. Ricci, T. Inose, R. Aubert, G. Lu, J. A. Hutchison, J. Hofkens, L. Latterini, H. Uji-i
    CHEMICAL COMMUNICATIONS 53 (37) 5121 - 5124 1359-7345 2017/05 [Refereed][Not invited]
    A novel one-step in situ synthesis of gold nanostars (AuNSs) on a pre-cured polydimethylsiloxane (PDMS) film is proposed for the fabrication of highly sensitive surface-enhanced Raman scattering (SERS) substrates. Plasmonic activity of the substrates was investigated by collecting SERS maps of 4-mercaptobenzoic acid (4-MBA). The applicability of these flexible substrates is further demonstrated by SERS-based pesticide detection on fruit skin.
  • Zhi Li, Hans Van Gorp, Peter Walke, Thanh Hai Phan, Yasuhiko Fujita, John Greenwood, Oleksandr Ivasenko, Kazukuni Tahara, Yoshito Tobe, Hiroshi Uji-, Stijn F. L. Mertens, Steven De Feyter
    NANOSCALE 9 (16) 5188 - 5193 2040-3364 2017/04 [Refereed][Not invited]
    Altering the chemical reactivity of graphene can offer new opportunities for various applications. Here, we report that monolayers of densely packed n-pentacontane significantly reduce the covalent grafting of aryl radicals to graphitic surfaces. The effect is highly local in nature and on fully covered substrates grafting can occur only at monolayer imperfections such as interdomain borders and vacancy defects. Grafting partially covered substrates primarily results in the covalent modification of uncoated areas.
  • Remko Aubert, Bart Kenens, Maha Chamtouri, Yasuhiko Fujita, Beatrice Fortuni, Gang Lu, James A. Hutchison, Tomoko Inose, Hiroshi Uji-I
    ACS Omega 2 (10) 6309 - 6313 2470-1343 2017 [Refereed][Not invited]
    Enhancement of visible-light photocurrent generation by sol-gel anatase TiO2 films was achieved by binding small polyol molecules to the TiO2 surface. Binding ethylene glycol onto the surface, enhancement factors up to 2.8 were found in visible-light photocurrent generation experiments. Density functional theory calculations identified midgap energy states that emerge as a result of the binding of a range of polyols to the TiO2 surface. The presence and energy of the midgap state is predicted to depend sensitively on the structure of the polyol, correlating well with the photocurrent generation results. Together, these results suggest a new, facile, and cost-effective route to precise surface band gap engineering of TiO2 toward visible-light-induced photocatalysis and energy storage.
  • Roald Phillipson, Cesar J. Lockhart de la Rosa, Joan Teyssandier, Peter Walke, Deepali Waghray, Yasuhiko Fujita, Jinne Adisoejoso, Kunal S. Mali, Inge Asselierghs, Cedric Huyghebaert, Hiroshi Uji-i, Stefan De Gendt, Steven De Feyter
    NANOSCALE 8 (48) 20017 - 20026 2040-3364 2016/12 [Refereed][Not invited]
    One current key challenge in graphene research is to tune its charge carrier concentration, i.e., p-and n-type doping of graphene. An attractive approach in this respect is offered by controlled doping via well-ordered self-assembled networks physisorbed on the graphene surface. We report on tunable n-type doping of graphene using self-assembled networks of alkyl-amines that have varying chain lengths. The doping magnitude is modulated by controlling the density of the strong n-type doping amine groups on the surface. As revealed by scanning tunneling and atomic force microscopy, this density is governed by the length of the alkyl chain which acts as a spacer within the self-assembled network. The modulation of the doping magnitude depending on the chain length was demonstrated using Raman spectroscopy and electrical measurements on graphene field effect devices. This supramolecular functionalization approach offers new possibilities for controlling the properties of graphene and other two-dimensional materials at the nanoscale.
  • Rebeca Sola-Llano, Virginia Martinez-Martinez, Yasuhiko Fujita, Luis Gomez-Hortigueela, Almudena Alfayate, Hiroshi Uji-i, Eduard Fron, Joaquin Perez-Pariente, Inigo Lopez-Arbeloa
    CHEMISTRY-A EUROPEAN JOURNAL 22 (44) 15700 - 15711 0947-6539 2016/10 [Refereed][Not invited]
    In this work, hemicyanine dye LDS722 is encapsulated into the 1D elliptical nanochannels of MgAPO-11 aluminophosphate by a crystallization inclusion method. The synthesis of the hybrid material has been optimized through a systematic variation of the crystallization conditions in order to obtain pure and large crystals (around 20mx30m) suitable for optical applications. The tight fitting between the molecular size of the guest dye and the pore dimensions of the host has favored a rigid planar conformation of the dye, restricting its inherent flexibility, which is confirmed by molecular simulations. Consequently, the encapsulation of LDS722 into MgAPO-11 has led to an astonishing enhancement of the fluorescence with respect to the dye into MgAPO-5, with slightly larger cylindrical channels, and with respect to the dye in solution. Moreover, the perfect alignment of LDS722 (dye with intrinsic nonlinear-optical properties) along the channels of MgAPO-11 has revealed attractive second-order nonlinear properties, such as second harmonic generation, proven through microscopy measurements in single crystals.
  • Yasuhiko Fujita, Peter Walke, Steven De Feyter, Hiroshi Uji-i
    JAPANESE JOURNAL OF APPLIED PHYSICS 55 (8) 0021-4922 2016/08 [Refereed][Not invited]
    Tip-enhanced Raman scattering (TERS) microscopy is a promising technique for use in surface analysis, allowing both topographic and spectroscopic information to be obtained simultaneously at a scale below 10 nm. One proposed method to further improve spatial resolution is the use of propagating surface plasmons as an excitation light source (i.e.,remote excitation). However, this requires a specialized tip that can only be fabricated via expensive procedures, such as electron-beam lithography. Here, we propose a new method for fabricating silver nanowire-based tips that are suitable for remote excitation-TERS, removing the need for such techniques. A silver nanowire was fixed onto a tungsten-tip using a micromanipulator, before gold nanoparticles were attached in a site-specific manner using AC-dielectrophoresis. All the processes were completed using an optical microscope in the ambient. The background intensities in TERS spectra were suppressed with remote excitation relative to the conventional excitation configuration, indicating an increase in TERS sensitivity. (C) 2016 The Japan Society of Applied Physics.
  • Yasuhiko Fujita, Peter Walke, Steven De Feyter, Hiroshi Uji-i
    JAPANESE JOURNAL OF APPLIED PHYSICS 55 (8) 0021-4922 2016/08 [Refereed][Not invited]
    Tip-enhanced Raman scattering (TERS) microscopy is a technique that combines the chemical sensitivity of Raman spectroscopy with the resolving power of scanning probe microscopy. The key component of any TERS setup is a plasmonically-active noble metal tip, which serves to couple far-field incident radiation with the near-field. Thus, the design and implementation of reproducible probes are crucial for the continued development of TERS as a tool for nanoscopic analysis. Here we discuss conventional methods for the fabrication of TERS-ready tips, highlighting the problems therein, as well as detailing more recent developments to improve reducibility. In addition, the idea of remote excitation-TERS is enlightened upon, whereby TERS sensitivity is further improved by using propagating surface plasmons to separate the incident radiation from the tip apex, as well as how this can be incorporated into the fabrication process. (C) 2016 The Japan Society of Applied Physics
  • Damiano Genovese, Alessandro Aliprandi, Eko A. Prasetyanto, Matteo Mauro, Michael Hirtz, Harald Fuchs, Yasuhiko Fujita, Hiroshi Uji-, Sergei Lebedkin, Manfred Kappes, Luisa De Cola
    ADVANCED FUNCTIONAL MATERIALS 26 (29) 5271 - 5278 1616-301X 2016/08 [Refereed][Not invited]
    A Pt(II) complex, bearing an oligo-ethyleneoxide pendant, is able to self-assemble in ultralong ribbons that display mechanochromism upon nanoscale mechanical stimuli, delivered through atomic force microscopy (AFM). Such observation paves the way to fine understanding and manipulation of the mechanochromic properties of such material at the nanoscale. AFM allows quantitative assessment of nanoscale mechanochromism as arising from static pressure (piezochromism) and from shear-based mechanical stimuli (tribochromism), and to compare them with bulk pressure-dependent luminescence observed with diamond-anvil cell (DAC) technique. Confocal spectral imaging reveals that mechanochromism only takes place within short distance from the localized mechanical stimulation, which allows to design high-density information writing with AFM nanolithography applied on individual self-assembled ribbons. Each ribbon hence serves as an individual microsystem for data storage. The orange luminescence of written information displays high contrast compared to cyan native luminescence; moreover, it can be selectively excited with visible light. In addition, ribbons show photochromism, i.e., the emission spectrum changes upon exposure to light, in a similar way as upon mechanical stress. Photochromism is here conveniently used to conceal and eventually erase information previously written with nanolithography by irradiation.
  • Hannelore Bove, Christian Steuwe, Eduard Fron, Eli Slenders, Jan D'Haen, Yasuhiko Fujita, Hiroshi Uji-i, Martin vandeVen, Maarten Roeffaers, Marcel Ameloot
    NANO LETTERS 16 (5) 3173 - 3178 1530-6984 2016/05 [Refereed][Not invited]
    Although adverse health effects of carbon black (CB) exposure are generally accepted, a direct, label-free approach for detecting CB particles in fluids and at the cellular level is still lacking. Here, we report nonincandescence related white-light (WL) generation by dry and suspended carbon black particles under illumination with femtosecond (fs) pulsed near-infrared light as a powerful tool for the detection of these carbonaceous materials. This observation is done for four different CB species with diameters ranging from 13 to 500 nm, suggesting this WL emission under fs near-infrared illumination is a general property of CB particles. As the emitted radiation spreads over the whole visible spectrum, detection is straightforward and flexible. The unique property of the described WL emission allows optical detection and unequivocal localization of CB particles in fluids and in cellular environments while simultaneously colocalizing different cellular components using various specific fluorophores as shown here using human lung fibroblasts. The experiments are performed on a typical multiphoton laser-scanning microscopy platform, widely available in research laboratories.
  • Yasuhiko Fujita, Peter Walke, Gang Lu, Maha Chamtouri, Steven De Feyter, Hiroshi Uji-i
    ADVANCED MATERIALS TECHNOLOGIES 1 (2) 2365-709X 2016/05 [Refereed][Not invited]
  • Haifeng Yuan, Elke Debroye, Kris Janssen, Hiroyuki Naiki, Christian Steuwe, Gang Lu, Michele Moris, Emanuele Orgiu, Hiroshi Uji-i, Frans De Schryver, Paolo Samori, Johan Hofkens, Maarten Roeffaers
    JOURNAL OF PHYSICAL CHEMISTRY LETTERS 7 (3) 561 - 566 1948-7185 2016/02 [Refereed][Not invited]
    Organometal halide perovskites show promising features for cost-effective application in photovoltaics. The material instability remains a major obstacle to broad application because of the poorly understood degradation pathways. Here, we apply simultaneous luminescence and electron microscopy on perovskites for the first time, allowing us to monitor in situ morphology evolution and optical properties upon perovskite degradation. Interestingly, morphology, photoluminescence (PL), and cathodoluminescence of perovskite samples evolve differently upon degradation driven by electron beam (e-beam) or by light. A transversal electric current generated by a scanning electron beam leads to dramatic changes in PL and tunes the energy band gaps continuously alongside film thinning. In contrast, light-induced degradation results in material decomposition to scattered particles and shows little PL spectral shifts. The differences in degradation can be ascribed to different electric currents that drive ion migration. Moreover, solution-processed perovskite cuboids show heterogeneity in stability which is likely related to crystallinity and morphology. Our results reveal the essential role of ion migration in perovskite degradation and provide potential avenues to rationally enhance the stability of perovskite materials by reducing ion migration while improving morphology and crystallinity. It is worth noting that even moderate e-beam currents (86 pA) and acceleration voltages (10 kV) readily induce significant perovskite degradation and alter their optical properties. Therefore, attention has to be paid while characterizing such materials using scanning electron microscopy or transmission electron microscopy techniques.
  • Liang Su, Haifeng Yuan, Gang Lu, Susana Rocha, Michel Orrit, Johan Hofkens, Hiroshi Uji-i
    ACS NANO 10 (2) 2455 - 2466 1936-0851 2016/02 [Refereed][Not invited]
    Optical antennas made of metallic nanostructures dramatically enhance single-molecule fluorescence to boost the detection sensitivity. Moreover, emission properties detected at the optical far field are dictated by the antenna. Here we study the emission from molecule antenna hybrids by means of super resolution localization and defocused imaging. Whereas gold nanorods make single-crystal violet molecules in the tip's vicinity visible in fluorescence, super-resolution localization on the enhanced molecular fluorescence reveals geometrical centers of the nanorod antenna instead. Furthermore, emission angular distributions of dyes linked to the nanorod surface resemble that of nanorods in defocused imaging. The experimental observations are consistent with numerical calculations using the finite-difference time-domain method.
  • Masoumeh Keshavarz, Hans Engelkamp, Jialiang Xu, Els Braeken, Matthijs B. J. Otten, Hiroshi Uji-i, Erik Schwartz, Matthieu Koepf, Anja Vananroye, Jan Vermant, Roeland J. M. Nolte, Frans De Schryver, Jan C. Maan, Johan Hofkens, Peter C. M. Christianen, Alan E. Rowan
    ACS NANO 10 (1) 1434 - 1441 1936-0851 2016/01 [Refereed][Not invited]
    The thermal motion of polymer chains in a crowded environment is anisotropic and highly confined. Whereas theoretical and experimental progress has been made, typically only indirect evidence of polymer dynamics is obtained either from scattering or mechanical response. Toward a complete understanding of the complicated polymer dynamics in crowded media such as biological cells, it is of great importance to unravel the role of heterogeneity and molecular individualism. In the present work, we investigate the dynamics of synthetic polymers and the tube-like motion of individual chains using time resolved fluorescence microscopy. A single fluorescently labeled polymer molecule is observed in a sea of unlabeled polymers, giving access to not only the dynamics of the probe chain itself but also to that of the surrounding network. We demonstrate that it is possible to extract the characteristic time constants and length scales in one experiment, providing a detailed understanding of polymer dynamics at the single chain level. The quantitative agreement with bulk rheology measurements is promising for using local probes to study heterogeneity in complex, crowded systems.
  • Somia Rahmoun, Fabrice Mairesse, Hiroshi Uji-i, Johan Hofkens, Tadeusz Sliwa
    IMAGE AND SIGNAL PROCESSING (ICISP 2016) 9680 79 - 88 0302-9743 2016 [Refereed][Not invited]
    In the molecular field, researchers analyze dynamics of polymers by microscopy: several measurements such as length and curvature are performed in their studies. To achieve correct analysis they need to extract the curve representing as good as possible the observed polymer shape which is a grayscale thick curve with noise and blur. We propose, in this paper, a method to extract such a curve. A polymer chain moves in a snake-like fashion (Reptation): it can self-intersect and form several complex geometries. To efficiently extract the different geometries, we generate the curve by computing a piecewise centerline browsing the shape by geodesics: each shape gives a set of separate geodesics. By fusion, we obtain the complete curve traveling the shape. To keep the correct curve orientation, the fusion is considered as a graph traversal problem. Promising results show that the extracted curve properly represents the shape and can be used for polymer study.
  • Bart Kenens, Maha Chamtouri, Remko Aubert, Kana Miyakawa, Yasufumi Hayasaka, Hiroyuki Naiki, Hiroki Watanabe, Tomoko Inose, Yasuhiko Fujita, Gang Lu, Akito Masuhara, Hiroshi Uji-i
    RSC ADVANCES 6 (100) 97464 - 97468 2046-2069 2016 [Refereed][Not invited]
    Metal nanoparticle photo-deposition on TiO2 enhances the semiconductor catalytic activity. We show for the first time that strong adsorption of simple diol-molecules improves the photo-deposition, by introducing a TiO2 midgap state and blocking active sites. The resulting photo-deposited gold nanoparticles are mono-dispersed and well-distributed over the TiO2 particles. The photo-catalytic activity of the Au/TiO2 systems obtained in ethyleneglycol was significantly enhanced compared to those prepared in conventional solvents, such as water and ethanol.
  • Koen Kennes, Peter Dedecker, James A. Hutchison, Eduard Fron, Hiroshi Uji-I, Johan Hofkens, Mark Van Der Auweraer
    ACS Omega 1 (6) 1383 - 1392 2470-1343 2016 [Refereed][Not invited]
    The fluorescence intermittency or “blinking” of single molecules of ATTO647N (ATTO) in the conductive matrix polyvinylcarbazole (PVK) is described in the presence of an external applied electric field. It is shown that due to the energy distribution of the highest occupied molecular orbital (HOMO) level of PVK, which is energetically close to the HOMO of ATTO, sporadic electron transfer occurs. As a result, the on/off dynamics of blinking can be influenced by the electric field. This field will, depending on the respective position and orientation of the dye/polymer system with respect to those of the electrodes, either enhance or suppress electron transfer from PVK to ATTO as well as the back electron transfer from reduced ATTO to PVK. After the charge-transfer step, the applied field will pull the hole in PVK away from the dye, increasing the overall time the dye resides in a dark state.
  • Eduard Fron, Herlinde De Keersmaecker, Susana Rocha, Yannick Baeten, Gang Lu, Hiroshi Uji-, Mark Van der Auweraer, Johan Hofkens, Hideaki Mizuno
    JOURNAL OF PHYSICAL CHEMISTRY B 119 (47) 14880 - 14891 1520-6106 2015/11 [Refereed][Not invited]
    LSSmOrange is a fluorescent protein with a large energy gap between the absorption and emission bands (5275 cm(-1)). The electronic structure of the LSSmOrange chromophore, 2-[(5-)-2-hydroxy-dihydrooxazole]-4-(p-hydroxybenzylidene)-5-imidazolinone, is affected by deprotonation of the p-hydroxybenzylidene group. We investigated LSSmOrange by time-resolved spectroscopy in the femtosecond and nanosecond range. The ground state chromophore was almost exclusively in the neutral form, which had a main absorption band at 437 nm with a small shoulder at 475 nm. The absorption at a wavelength within the former band promoted the protein to the excited state where excited state proton transfer (ESPT) could lead to deprotonation in 0.8 ps. Following ESPT, the chromophore emitted fluorescence with a maximum at 573 nm and a decay time of 3500 ps. Although deprotonation by ESPT occurs, we unexpectedly found a slow accumulation of the anionic form in the ground state upon repeated high intensity excitation. This accumulation of the anionic form was accompanied by a shift of the absorption band to 553 nm without changing the emission band. MALDI-MS revealed that this shift is accompanied by decarboxylation of E222, which is interacting with the imidazolinone ring of the chromophore. We concluded that the photoinduced decarboxylation induced a conformational change that affected local environment around the hydroxyl group, resulting in a stable deprotonated form of the chromophore.
  • John Greenwood, Thanh Hai Phan, Yasuhiko Fujita, Zhi Li, Oleksandr Lvasenko, Willem Vanderlinden, Hans Van Gorp, Wout Frederickx, Gang Lu, Kazukuni Tahara, Yoshito Tobe, Hiroshi Uji-i, Stijn F. L. Mertens, Steven De Feyter
    ACS NANO 9 (5) 5520 - 5535 1936-0851 2015/05 [Refereed][Not invited]
    We shine light on the covalent modification of graphite and graphene substrates using diazonium chemistry under ambient conditions. We report on the nature of the chemical modification of these graphitic substrates, the relation between molecular structure and film morphology, and the impact of the covalent modification on the properties of the substrates, as revealed by local microscopy and spectroscopy techniques and electrochemistry. By careful selection of the reagents and optimizing reaction conditions, a high density of covalently grafted molecules is obtained, a result that is demonstrated in an unprecedented way by scanning tunneling microscopy (STM) under ambient conditions. With nanomanipulation, i.e., nanoshaving using STM, surface structuring and functionalization at the nanoscale is achieved. This manipulation leads to the removal of the covalently anchored molecules, regenerating pristine sp(2) hybridized graphene or graphite patches, as proven by space-resolved Raman microscopy and molecular self-assembly studies.
  • Liang Su, Gang Lu, Bart Kenens, Susana Rocha, Eduard Fron, Haifeng Yuan, Chang Chen, Pol Van Dorpe, Maarten B. J. Roeffaers, Hideaki Mizuno, Johan Hofkens, James A. Hutchison, Hiroshi Uji-i
    NATURE COMMUNICATIONS 6 2041-1723 2015/02 [Refereed][Not invited]
    The enhancement of molecular absorption, emission and scattering processes by coupling to surface plasmon polaritons on metallic nanoparticles is a key issue in plasmonics for applications in (bio) chemical sensing, light harvesting and photocatalysis. Nevertheless, the point spread functions for single-molecule emission near metallic nanoparticles remain difficult to characterize due to fluorophore photodegradation, background emission and scattering from the plasmonic structure. Here we overcome this problem by exciting fluorophores remotely using plasmons propagating along metallic nanowires. The experiments reveal a complex array of single-molecule fluorescence point spread functions that depend not only on nanowire dimensions but also on the position and orientation of the molecular transition dipole. This work has consequences for both single-molecule regime-sensing and super-resolution imaging involving metallic nanoparticles and opens the possibilities for fast size sorting of metallic nanoparticles, and for predicting molecular orientation and binding position on metallic nanoparticles via far-field optical imaging.
  • Haifeng Yuan, Kris P. F. Janssen, Thomas Franklin, Gang Lu, Liang Su, Xian Gu, Hiroshi Uji-i, Maarten B. J. Roeffaers, Johan Hofkens
    RSC ADVANCES 5 (9) 6829 - 6833 2046-2069 2015 [Refereed][Not invited]
    We report an investigation on the effect of stabilization agents and surface curvatures on oxidative etching of three classes of anisotropically shaped gold nanoparticles namely, rods, bipyramids and prisms. In particular, the dual role of the stabilizing agent CTAB in the etching process is explored, showing how it acts both as a source of bromine ions, accelerating etching and as a protection agent, resulting in anisotropic reshaping.
  • Corinna Raimondo, Bart Kenens, Federica Reinders, Marcel Mayor, Hiroshi Uji-i, Paolo Samori
    NANOSCALE 7 (33) 13836 - 13839 2040-3364 2015 [Refereed][Not invited]
    pi-pi Intermolecular interactions among adjacent conjugated azobenzenes chemisorbed on (non-) flat Au surfaces can be tuned by varying the curvature of the Au nanoparticles. Here we show that such interactions rule the thermal cis-trans isomerization kinetics, towards a better control on the azobenzene bistability for its optimal integration as a responsive material.
  • Min Li, Duncan den Boer, Patrizia Iavicoli, Jinne Adisoejoso, Hiroshi Uji-i, Mark Van der Auweraer, David B. Amabilino, Johannes A. A. W. Elemans, Steven De Feyter
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 136 (50) 17418 - 17421 0002-7863 2014/12 [Refereed][Not invited]
    Changing abruptly the potential between a scanning tunneling microscope tip and a graphite substrate induces "high-conductance" spots at the molecular level in a monolayer formed by a manganese chloride-porphyrin molecule. These events are attributed to the pulse-induced formation of mu-oxo-porphyrin dimers. The pulse voltage must pass a certain threshold for dimer formation, and pulse polarity determines the yield.
  • Kuan-Lin Liu, Alexey V. Kubarev, Jordi Van Loon, Hiroshi Uji-i, Dirk E. De Vos, Johan Hofkens, Maarten B. J. Roeffaers
    ACS NANO 8 (12) 12650 - 12659 1936-0851 2014/12 [Refereed][Not invited]
    Dealuminated zeolites are widely used acid catalysts in research and the chemical industry. Bulk-level studies have revealed that the improved catalytic performance results from an enhanced molecular transport as well as from changes in the active sites. However, fully exploiting this information in rational catalyst design still requires insight in the intricate interplay between both. Here we introduce fluorescence and stimulated Raman scattering microscopy to quantify subcrystal reactivity as well as acid site distribution and to probe site accessibility in the set of individual mordenite zeolites. Dealumination effectively introduces significant heterogeneities between different particles and even within individual crystals. Besides enabling direct rationalization of the nanoscale catalytic performance, these observations reveal valuable information on the industrial dealumination process itself.
  • Yasuhiko Fujita, Rie Chiba, Gang Lu, Noriko N. Horimoto, Shinji Kajimoto, Hiroshi Fukumura, Hiroshi Uji-
    CHEMICAL COMMUNICATIONS 50 (69) 9839 - 9841 1359-7345 2014/09 [Refereed][Not invited]
    A chemically synthesized silver nanowire was used for atomic-resolution STM imaging and tip-enhanced Raman scattering (TERS) spectroscopy, yielding excellent reproducibility. This TERS tip will open a new venue to surface analysis, such as molecular finger printing at nanoscales.
  • Gang Lu, Herlinde De Keersmaecker, Liang Su, Bart Kenens, Susana Rocha, Eduard Fron, Chang Chen, Pol Van Dorpe, Hideaki Mizuno, Johan Hofkens, James A. Hutchison, Hiroshi Uji-i
    ADVANCED MATERIALS 26 (30) 5124 - 5128 0935-9648 2014/08 [Refereed][Not invited]
  • Robrecht M. A. Vergauwe, Hiroshi Uji-i, Karen De Ceunynck, Jan Vermant, Karen Vanhoorelbeke, Johan Hofkens
    JOURNAL OF PHYSICAL CHEMISTRY B 118 (21) 5660 - 5669 1520-6106 2014/05 [Refereed][Not invited]
    The von Willebrand factor (VWF) is a human plasma protein that plays a key role in the initiation of the formation of thrombi under high shear stress in both normal and pathological situations. It is believed that VWF undergoes a conformational transition from a compacted, globular to an extended form at high shear stress. In this paper, we develop and employ an approach to visualize the large-scale conformation of VWF in a (pressure-driven) Poiseuille flow of water-glycerol buffers with wide-field single molecule fluorescence microscopy as a function of shear stress. Comparison of the imaging results for VWF with the results of a control with lambda-phage double-stranded DNA shows that the detection of individual VWF multimers in flow is feasible. A small fraction of VWF multimers are observed as visibly extended along one axis up to lengths of 2.0 mu m at high applied shear stresses. The size of this fraction of molecules seems to exhibit an apparent dependency on shear stress. We further demonstrate that the obtained results are independent of the charge of the fluorophore used to label VWF. The obtained results support the hypothesis of the conformational extension of VWF in shear flow.
  • Susana Rocha, Herlinde De Keersmaecker, James A. Hutchison, Karen Vanhoorelbeke, Johan A. Martens, Johan Hofkens, Hiroshi Uji-i
    LANGMUIR 30 (16) 4743 - 4751 0743-7463 2014/04 [Refereed][Not invited]
    Important cellular events such as division require drastic changes in the shape of the membrane. These remodeling processes can be triggered by the binding of specific proteins or by changes in membrane composition and are linked to phospholipid metabolism for which dedicated enzymes, named phospholipases, are responsible. Here wide-field fluorescence microscopy is used to visualize shape changes induced by the action of phospholipase A1 on dye-labeled supported membranes of POPC (1-palmitoyl-2-oleolysn-glycero-3-phosphocholine). Time-lapse imaging demonstrates that layers either shrink and disappear or fold and collapse into vesicles. These vesicles can undergo further transformations such as budding, tubulation, and pearling within 5 min of formation. Using dye-labeled phospholipases, we can monitor the presence of the enzyme at specific positions on the membrane as the shape transformations occur. Furthermore, incorporating the products of hydrolysis into POPC membranes is shown to induce transformations similar to those observed for enzyme action. The results suggest that phospholipase-mediated hydrolysis plays an important role in membrane transformations by altering the membrane composition, and a model is proposed for membrane curvature based on the presence and shape of hydrolysis products.
  • Karen De Ceunynck, Susana Rocha, Simon F. De Meyer, J. Evan Sadler, Hiroshi Uji-i, Hans Deckmyn, Johan Hofkens, Karen Vanhoorelbeke
    JOURNAL OF BIOLOGICAL CHEMISTRY 289 (13) 8903 - 8915 0021-9258 2014/03 [Refereed][Not invited]
    Background: ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type-1 repeats) cleaves pro-thrombotic ultra-large von Willebrand factor (VWF) strings. Results: Customized single particle tracking enabled visualization of single ADAMTS13 enzymes that bind to long platelet-decorated VWF strings. Conclusion: ADAMTS13 readily bind to multiple available sites on VWF strings. Significance: Single molecule imaging can be used to study interactions between enzymes and large biopolymers in flow. von Willebrand factor (VWF) strings are removed from the endothelial surface by ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type-1 repeats)-mediated proteolysis. To visualize how single ADAMTS13 molecules bind to these long strings, we built a customized single molecule fluorescence microscope and developed single particle tracking software. Extensive analysis of over 6,000 single inactive ADAMTS13(E225Q) enzymes demonstrated that 20% of these molecules could be detected in at least two consecutive 60-ms frames and followed two types of trajectories. ADAMTS13(E225Q) molecules either decelerated in the vicinity of VWF strings, whereas sometimes making brief contact with the VWF string before disappearing again, or readily bound to the VWF strings and this for 120 ms or longer. These interactions were observed at several sites along the strings. Control experiments using an IgG protein revealed that only the second type of trajectory reflected a specific interaction of ADAMTS13 with the VWF string. In conclusion, we developed a dedicated single molecule fluorescence microscope for detecting single ADAMTS13 molecules (nm scale) on their long, flow-stretched VWF substrates (m scale) anchored on living cells. Comprehensive analysis of all detected enzymes showed a random interaction mechanism for ADAMTS13 with many available binding sites on the VWF strings.
  • James A. Hutchison, Hiroshi Uji-i, Ania Deres, Tom Vosch, Susana Rocha, Sibylle Mueller, Andreas A. Bastian, Joerg Enderlein, Hassan Nourouzi, Chen Li, Andreas Herrmann, Klaus Muellen, Frans De Schryver, Johan Hofkens
    NATURE NANOTECHNOLOGY 9 (2) 131 - 136 1748-3387 2014/02 [Refereed][Not invited]
    Developing molecular systems with functions analogous to those of macroscopic machine components, such as rotors(1,2), gyroscopes(3) and valves(4), is a long-standing goal of nanotechnology. However, macroscopic analogies go only so far in predicting function in nanoscale environments, where friction dominates over inertia(5,6). In some instances, ratchet mechanisms have been used to bias the ever-present random, thermally driven (Brownian) motion and drive molecular diffusion in desired directions(7). Here, we visualize the motions of surface-bound molecular rotors using defocused fluorescence imaging, and observe the transition from hindered to free Brownian rotation by tuning medium viscosity. We show that the otherwise random rotations can be biased by the polarization of the excitation light field, even though the associated optical torque is insufficient to overcome thermal fluctuations. The biased rotation is attributed instead to a fluctuating-friction mechanism(8,9) in which photoexcitation of the rotor strongly inhibits its diffusion rate.
  • Liang Su, Haifeng Yuan, Gang Lu, Johan Hofkens, Maarten Roeffaers, Hiroshi Uji-i
    NANOPHOTONICS AND MICRO/NANO OPTICS II 9277 0277-786X 2014 [Refereed][Not invited]
    Fluorescence correlation spectroscopy (FCS), a powerful tool to resolve local properties, dynamical process of molecules, rotational and translational diffusion motions, relies on the fluctuations of florescence observables in the observation volume. In the case of rare transition events or small dynamical fluctuations, FCS requires few molecules or even single molecules in the observation volume at a time to minimize the background signals. Metal nanoparticle which possess unique localized surface plasmon resonance (LSPR) have been used to reduce the observation volume down to sub-diffraction limited scale while maintain at high analyst concentration up to tens of micromolar. Nevertheless, the applications of functionalized nanoparticles in living cell are limited due to the continuous diffusion after cell uptake, which makes it difficult to target the region of interests in the cell. In this work, we demonstrate the use of silver nanowires for remote excitation FCS on fluorescent molecules in solution. By using propagation surface plasmon polaritons (SPPs) which supported by the silver nanowire to excite the fluorescence, both illumination and observation volume can be reduced simultaneously. In such a way, less perturbation is induced to the target region, and this will broaden the application scope of silver nanowire as tip in single cell endoscopy.
  • ADAMTS13 meets von Willebrand factor strings: a single molecule approach
    De Ceunynck K. E. P, Rocha S. N, De Meyer S. F, Uji-I H, Deckmyn H, Hofkens J, Vanhoorelbeke K
    JOURNAL OF THROMBOSIS AND HAEMOSTASIS 11 120 - 121 1538-7933 2013/07 [Refereed][Not invited]
  • Luminita Marin, Maria-Cristina Popescu, Andrei Zabulica, Hiroshi Uji-, Eduard Fron
    CARBOHYDRATE POLYMERS 95 (1) 16 - 24 0144-8617 2013/05 [Refereed][Not invited]
    The obtaining of bio-polymer dispersed liquid crystal (bio-PDLC) systems based on a chitosan polymer matrix is reported here for the first time. The new PDLC composites have been obtained by encapsulation of 4-cyano-4'-pentylbiphenyl (5CB) as low molecular weight liquid crystal into chitosan, and they have been characterized by polarized optical microscopy, differential scanning calorimetry, electron and transmission scanning microscopy, Raman and fluorescence spectroscopy. Submicrometric liquid crystalline droplets with uniform size distribution and density have been obtained for low liquid crystal content into the PDLCs. The droplets have a radial configuration being anchored into chitosan matrix by an interface ordering coupling phenomenon. (C) 2013 Elsevier Ltd. All rights reserved.
  • Takanori Tada, Yukiteru Katsumoto, Karel Goossens, Hiroshi Uji-i, Johan Hofkens, Tatsuya Shoji, Noboru Kitamura, Yasuyuki Tsuboi
    JOURNAL OF PHYSICAL CHEMISTRY C 117 (20) 10818 - 10824 1932-7447 2013/05 [Refereed][Not invited]
    We discovered for aqueous thermoresponsive polymer solutions that only a slight change in stereoregularity of the polymer can drastically accelerate phase separation. Single molecule fluorescence tracking (SMT) for an isotactic-slight-rich (meso-diad-rich) polymer sample solution revealed an interpolymer nanonetwork even before phase separation, and also revealed a novel phase in which translational molecular motion was frozen after phase separation. For such systems, fluorescence correlation spectroscopy (FCS) provided quantitative information on molecular diffusion. The results on FCS well agreed with the interpolymer nanonetwork model that was proposed on the-basis of SMT measurement. We demonstrate such a novel method to control phase separation dynamics and also the interpolymer nanonetwork model.
  • Jialiang Xu, Sergey Semin, Dorota Niedzialek, Paul H. J. Kouwer, Eduard Fron, Eduardo Coutino, Matteo Savoini, Yuliang Li, Johan Hofkens, Hiroshi Uji-, David Beljonne, Theo Rasing, Alan E. Rowan
    ADVANCED MATERIALS 25 (14) 2084 - 2089 0935-9648 2013/04 [Refereed][Not invited]
    While highly desired in integrated optical circuits, multiresponsive and tunable nonlinear optical (NLO) active 1D (sub) wavelength scale superstructures from organic materials are rarely reported due to the strong tendency of organic molecules to self-assembly in centrosymmetric modes. Here a solution-processed assembly approach is reported to generate non-centrosymmetric single-crystalline organic microfibers with a cumulative dipole moment for anisotropic combined second-and third-order NLO.
  • Bart Kenens, Maksym Rybachuk, Johan Hofkens, Hiroshi Uji-I
    Journal of Physical Chemistry C 117 (6) 2547 - 2553 1932-7447 2013/02/14 [Refereed][Not invited]
    Metallic nanowires constitute a distinctive class of nanostructures that are able to guide surface plasmons in subwavelength dimensions. The effective use of light in- and out-coupling in low dimensional systems, such as excitation of surface plasmon polaritons along metallic nanowires, has been proposed to reduce physical dimensions of opto-electronic and nano-optical components and for high-resolution microscopy applications. Our investigation of light in- and out-coupling on silver nanowire systems by scanning optical coupling microscopy (SOCM) performed in combination with atomic force microscopy (AFM) revealed that the maximum coupling was obtained when the exciting laser light is projected at the end of the nanowire with a positioning accuracy of approximately 100 nm. Furthermore, it was found that a nanoparticle positioned at the end of a nanowire imparts an enhanced (by almost the factor of 4) plasmon in- and out-coupling light efficiency as compared to a free nanowire under the same excitation conditions. These findings are supported by theoretical simulations, which in addition provide a correlation between the nanoparticle size and the out-coupling light efficiency. Our investigations demonstrate that a combination of SOCM and AFM methods provide reliable qualitative and quantitative evaluation of plasmon in- and out-coupling characteristics on metallic nanowire systems. © 2012 American Chemical Society.
  • Aniruddha Paul, Bart Kenens, Johan Hofkens, Hiroshi Uji-i
    LANGMUIR 28 (24) 8920 - 8925 0743-7463 2012/06 [Refereed][Not invited]
    In this contribution, we report an effective and relatively simple route to grow triangular flat-top silver nanoparticles (NPs) directly on a solid substrate from smaller NPs through a wet photochemical synthesis. The method consists of fixing small, preformed nanotriangles (NTs) on a substrate and subsequently irradiating them with light in a silver seed solution. Furthermore, the use of linearly polarized light allows for exerting control on the growth direction of the silver nanotriangles on the substrate. Evidence for the role of surface plasmon resonances in governing the growth of the NTs is obtained by employing linear polarized light. Thus, this study demonstrates that light-induced, directional synthesis of nanoparticles on solid substrates is in reach, which is of utmost importance for plasmonic applications.
  • Hongzhen Lin, Silvia P. Centeno, Liang Su, Bart Kenens, Susana Rocha, Michel Sliwa, Johan Hofkens, Hiroshi Uji-i
    CHEMPHYSCHEM 13 (4) 973 - 981 1439-4235 2012/03 [Refereed][Not invited]
    Photoactivation localization microscopy (PALM) was applied to study surface-enhanced fluorescence (SEF) on metal nanostructures (SEF-PALM). The detection of fluorescence from individual single molecules can be used to image the point-spread-function and spatial distribution of the fluorescence emitted in the vicinity of a metal surface. Due to the strong scattering effect, the angular distribution of the fluorescence is altered by metals, resulting in a spatial shift of fluorescence spots with respect to the metal nanostructures, and has to be taken into account in the analysis. SEF-PALM can be used to discriminate effects of labelling density when estimating the enhancement factor in SEF. Furthermore, nanostructures with sizes below the diffraction limit can be resolved using this technique. SEF-PALM is established as a powerful tool to study plasmon-mediated phenomena on metal nanostructures.
  • Katrien G. M. Laurier, Michel Poets, Frederik Vermoortele, Gert De Cremer, Johan A. Martens, Hiroshi Uji-i, Dirk E. De Vos, Johan Hofkens, Maarten B. J. Roeffaers
    CHEMICAL COMMUNICATIONS 48 (10) 1559 - 1561 1359-7345 2012 [Refereed][Not invited]
    We report a one-step photocatalytic synthesis method of dendritic silver nanostructures. These self-organised structures show an excellent Raman enhancement enabling the detection of analytes from dilute solutions by surface-enhanced Raman spectroscopy.
  • Jian Ye, James Andell Hutchison, Hiroshi Uji-i, Johan Hofkens, Liesbet Lagae, Guido Maes, Gustaaf Borghs, Pol Van Dorpe
    NANOSCALE 4 (5) 1606 - 1611 2040-3364 2012 [Refereed][Not invited]
    Detailed understanding of the underlying mechanisms of surface enhanced Raman scattering (SERS) remains challenging for different experimental conditions. We report on an excitation wavelength dependent SERS of 4-aminothiophenol molecules on gold nanorings. SERS and normal Raman spectra, combined with well-characterized surface morphology, optical spectroscopy and electromagnetic (EM) field simulations of gold nanoring substrates indicate that the EM enhancement occurs at all three excitation wavelengths (532, 633 and 785 nm) employed but at short wavelengths (532 and 633 nm) charge transfer (CT) results in additional strong enhancements of particular Raman transitions. These results pave the way to further understanding the origin of the SERS mechanism.
  • Ania Deres, George A. Floudas, Klaus Muellen, Mark Van der Auweraer, Frans De Schryver, Joerg Enderlein, Hiroshi Uji-i, Johan Hofkens
    MACROMOLECULES 44 (24) 9703 - 9709 0024-9297 2011/12 [Refereed][Not invited]
    Single molecule defocused wide-field fluorescence microscopy (SMDWM) has been used to monitor the 3D reorientation of single molecules in a thin polymer film (similar to 300 nm) of monodisperse poly(n-butyl methacrylate) near the glass temperature (T-epsilon). Stroboscopic illumination allows for estimating reliable correlation times of single molecule rotational diffusion owing to the drastic lengthening of the observable trajectories. We demonstrate that homogeneity is restored similar to 19 K above the T-g determined with calorimetry. The rotational correlation times obtained from SMDWM show similar temperature dependence as the ones measured with established bulk measurements, such as dielectric spectroscopy and rheology, on the same polymer sample. Single molecular reorientation is coupled to the segmental rather than terminal relaxation of the surrounding polymer matrix. SMDWM revealed that spatial heterogeneity is more pronounced than temporal heterogeneity within the measurement time scale (hours to days), whereas this information is hidden in the bulk measurement.
  • Martin Lehmann, Susana Rocha, Bastien Mangeat, Fabien Blanchet, Hiroshi Uji-i, Johan Hofkens, Vincent Piguet
    PLOS PATHOGENS 7 (12) 1553-7366 2011/12 [Refereed][Not invited]
    Virus assembly and interaction with host-cell proteins occur at length scales below the diffraction limit of visible light. Novel super-resolution microscopy techniques achieve nanometer resolution of fluorescently labeled molecules. The cellular restriction factor tetherin (also known as CD317, BST-2 or HM1.24) inhibits the release of human immunodeficiency virus 1 (HIV-1) through direct incorporation into viral membranes and is counteracted by the HIV-1 protein Vpu. For super-resolution analysis of HIV-1 and tetherin interactions, we established fluorescence labeling of HIV-1 proteins and tetherin that preserved HIV-1 particle formation and Vpu-dependent restriction, respectively. Multicolor super-resolution microscopy revealed important structural features of individual HIV-1 virions, virus assembly sites and their interaction with tetherin at the plasma membrane. Tetherin localization to micro-domains was dependent on both tetherin membrane anchors. Tetherin clusters containing on average 4 to 7 tetherin dimers were visualized at HIV-1 assembly sites. Combined biochemical and super-resolution analysis revealed that extended tetherin dimers incorporate both N-termini into assembling virus particles and restrict HIV-1 release. Neither tetherin domains nor HIV-1 assembly sites showed enrichment of the raft marker GM1. Together, our super-resolution microscopy analysis of HIV-1 interactions with tetherin provides new insights into the mechanism of tetherin-mediated HIV-1 restriction and paves the way for future studies of virus-host interactions.
  • Karen De Ceunynck, Susana Rocha, Hendrik B. Feys, Simon F. De Meyer, Hiroshi Uji-i, Hans Deckmyn, Johan Hofkens, Karen Vanhoorelbeke
    JOURNAL OF BIOLOGICAL CHEMISTRY 286 (42) 36361 - 36367 0021-9258 2011/10 [Refereed][Not invited]
    Platelet-decorated von Willebrand factor (VWF) strings anchored to the endothelial surface are rapidly cleaved by ADAMTS13. Individual VWF string characteristics such as number, location, and auxiliary features of the ADAMTS13 cleavage sites were explored here using imaging and computing software. By following changes in VWF string length, we demonstrated that VWF strings are cleaved multiple times, successively shortening string length in the function of time and generating fragments ranging in size from 5 to over 100 mu m. These are larger than generally observed in normal plasma, indicating that further proteolysis takes place in circulation. Interestingly, in 89% of all cleavage events, VWF strings elongate precisely at the cleavage site before ADAMTS13 proteolysis. These local elongations are a general characteristic of VWF strings, independent of the presence of ADAMTS13. Furthermore, large elongations, ranging in size from 1.4 to 40 mu m, occur at different sites in space and time. In conclusion, ADAMTS13-mediated proteolysis of VWF strings under flow is preceded by large elongations of the string at the cleavage site. These elongations may lead to the simultaneous exposure of many exosites, thereby facilitating ADAMTS13-mediated cleavage.
  • Single molecule study of polymers
    Johan Hofkens, Hiroshi Uji-i
    ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 242 0065-7727 2011/08 [Refereed][Not invited]
  • Local stretching of VWF strings is a trigger for ADAMTS13 mediated proteolysis
    K. E. De Ceunynck, S. Rocha, H. B. Feys, S. F. De Meyer, H. Deckmyn, H. Uji-I, J. Hofkens, K. Vanhoorelbeke
    JOURNAL OF THROMBOSIS AND HAEMOSTASIS 9 308 - 308 1538-7933 2011/07 [Refereed][Not invited]
  • Hongzhen Lin, Tatsumi Ohta, Aniruddha Paul, James A. Hutchison, Kirilenko Demid, Oleg Lebedev, Gustaaf Van Tendeloo, Johan Hofkens, Hiroshi Uji-i
    JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY 221 (2-3) 220 - 223 1010-6030 2011/06 [Refereed][Not invited]
    This report describes the effect of light irradiation on the synthesis of silver nanowires by the well-known polyol method. High quality nanowires are produced in high yields when the reaction suspension is irradiated with 400-500 nm light during the nucleation stage. These studies suggest that light accelerates the formation of the nanoparticle seeds most appropriate for nanowire growth. (C) 2011 Published by Elsevier B.V.
  • Quantitative multicolour super-resolution microscopy reveals tetherin HIV-1 interaction
    M. Lehmann, S. Rocha, B. Mangeat, F. Blanchet, H. Uji-i, J. Hofkens, V. Piguet
    BRITISH JOURNAL OF DERMATOLOGY 164 (4) 918 - 918 0007-0963 2011/04 [Refereed][Not invited]
  • Rob Ameloot, Elena Gobechiya, Hiroshi Uji-i, Johan A. Martens, Johan Hofkens, Luc Alaerts, Bert F. Sels, Dirk E. De Vos
    ADVANCED MATERIALS 22 (24) 2685 - + 0935-9648 2010/06 [Refereed][Not invited]
    Processing metal organic frameworks with spatial and temporal control over crystal formation will increase the applicability of these highly porous materials. By exploiting solvent effects, stable synthesis solutions can be obtained, which can be used in combination with soft lithographic techniques to deposit oriented crystals in patterns by in situ crystallization (see figure).
  • Martin Gudmand, Susana Rocha, Nikos S. Hatzakis, Kalina Peneva, Klaus Muellen, Dimitrios Stamou, Hiroshi Uji-I, Johan Hofkens, Thomas Bjornholm, Thomas Heimburg
    BIOPHYSICAL JOURNAL 98 (9) 1873 - 1882 0006-3495 2010/05 [Refereed][Not invited]
    We monitored the action of phospholipase A(2) (PLA(2)) on L- and D-dipalmitoyl-phosphatidylcholine (DPPC) Langmuir monolayers by mounting a Langmuir-trough on a wide-field fluorescence microscope with single molecule sensitivity. This made it possible to directly visualize the activity and diffusion behavior of single PLA(2) molecules in a heterogeneous lipid environment during active hydrolysis. The experiments showed that enzyme molecules adsorbed and interacted almost exclusively with the fluid region of the DPPC monolayers. Domains of gel state L-DPPC were degraded exclusively from the gel-fluid interface where the buildup of negatively charged hydrolysis products, fatty acid salts, led to changes in the mobility of PLA(2). The mobility of individual enzymes on the monolayers was characterized by single particle tracking. Diffusion coefficients of enzymes adsorbed to the fluid interface were between 3.2 mu m(2)/s on the L-DPPC and 4.9 mu m(2)/s on the D-DPPC monolayers. In regions enriched with hydrolysis products, the diffusion dropped to approximate to 0.2 mu m(2)/s. In addition, slower normal and anomalous diffusion modes were seen at the L-DPPC gel domain boundaries where hydrolysis took place. The average residence times of the enzyme in the fluid regions of the monolayer and on the product domain were between approximate to 30 and 220 ms. At the gel domains it was below the experimental time resolution, i.e., enzymes were simply reflected from the gel domains back into solution.
  • Eduard Fron, Ania Deres, Susana Rocha, Gang Zhou, Klaus Muellen, Frans C. De Schryver, Michel Sliwa, Hiroshi Uji-i, Johan Hofkens, Tom Vosch
    JOURNAL OF PHYSICAL CHEMISTRY B 114 (3) 1277 - 1286 1520-6106 2010/01 [Refereed][Not invited]
    Insight into the exciton dynamics Occurring in a polyfluorene-perylenediimide (PF-PDI) copolymer with a reaction Mixture ratio of 100 fluorene units to 1 N,N'-bis(phenyl)-1,6,7,12-tetra(p-tert-octylphenoxy)-perylene-3,4,9,10-tetracarboxylic acid diimide (PDI) is presented here. Time-correlated single photon counting and femtosecond transient absorption spectroscopy measurements on the PF-PDI copolymer have been employed to investigate the excited-state properties of the polyfluorene subunit where the exciton is localized (PF) and the incorporated PDI chromophore. The experimental results were compared with those obtained from a polyfluorene polymer (model PF) and a N,N'-bis(2,6-diisopropylphenyl)-1,6,7,12-tetra(p-tert-octylphenoxy)perylene-14,91, I 0-tetracarboxylic acid diimide (model PDI) which were used as reference compounds. Because of the high polydispersity of the PF-PDI copolymer, there is a polymer fraction present that contains no PDI chromophores (polyfluorene polymer fraction (PIT polymer fraction)), and wide-field imaging of single polymers chains of the synthesized PF-PDI copolymer was used to estimate this PF polymer fraction. Following the primary excitation of the PIT in the PF-PDI copolymer, energy hopping between PF's can occur. A fraction of the energy of the absorbed photons will be transferred to a PDI chromophore via energy transfer from a PIT. In a polar solvent, a charge transfer state having the S, of the PDI moiety as a precursor state is found to form with high efficiency oil a nanosecond time scale. The data suggest that a fraction of the absorbed energy is directed, transferred, and used in charge separation, providing a clear view of a multistep mechanism of exciton dissociation into charges.
  • Kerstin Blank, Susana Rocha, Gert De Cremer, Maarten B. J. Roeffaers, Hiroshi Uji-i, Johan Hofkens
    SINGLE MOLECULE SPECTROSCOPY IN CHEMISTRY, PHYSICS AND BIOLOGY 96 495 - + 0172-6218 2010 [Refereed][Not invited]
    Single-molecule fluorescence experiments are a powerful tool to analyze reaction mechanisms of enzymes. Because of their unique potential to detect heterogeneities in space and time, they have provided unprecedented insights into the nature and mechanisms of conformational changes related to the catalytic reaction. The most important finding from experiments with single enzymes is the generally observed phenomenon that the catalytic rate constants fluctuate over time (dynamic disorder). These fluctuations originate from conformational changes occurring on time scales, which are similar to or slower than that of the catalytic reaction. Here, we summarize experiments with enzymes that show dynamic disorder and introduce new experimental strategies showing how single-molecule fluorescence experiments can be applied to address other open questions in medical and industrial enzymology, such as enzyme inactivation processes, reactant transfer in cascade reactions, and the mechanisms of interfacial catalysis.
  • Chang Chen, James Andell Hutchison, Pol Van Dorpe, Ronald Kox, Iwijn De Vlaminck, Hiroshi Uji-i, Johan Hofkens, Liesbet Lagae, Guido Maes, Gustaaf Borghs
    SMALL 5 (24) 2876 - 2882 1613-6810 2009/12 [Refereed][Not invited]
    The focusing of plasmons to obtain a strong and localized electromagnetic field enhancement for surface-enhanced Raman scattering (SERS) is increasing the interest in using plasmonic devices as molecular sensors. In this Full Paper, the successful fabrication and demonstration of a solid-state plasmonic nanoslit-cavity device equipped with nanoantennas on a freestanding thin silicon membrane as a substrate for SERS is reported. Numerical calculations predict a strong and spatially localized enhancement of the optical field in the nanoslit (6 nm in width) upon irradiation. The predicted enhancement factor of SERS was 5.3 x 10(5), localized in an area of just 6 x 1.5 nm(2). Raman spectroscopy and imaging confirm an enhancement factor of approximate to 10(6) for SERS from molecules chemisorbed at the nanoslit, and demonstrate the electromagnetic-field-enhancing function of the plasmonic nanoantennas. The freestanding membrane is open on both sides of the nanoslit, offering the potential for through-slit molecular translocation studies, and opening bright new perspectives for SERS applications in real-time (bio)chemical analysis.
  • Tom Vosch, Eduard Fron, Jun-ichi Hotta, Ania Deres, Hiroshi Uji-i, Abdenacer Idrissi, Jaesung Yang, Dongho Kim, Larissa Puhl, Andreas Haeuseler, Klaus Muellen, Frans C. De Schryver, Michel Sliwa, Johan Hofkens
    JOURNAL OF PHYSICAL CHEMISTRY C 113 (27) 11773 - 11782 1932-7447 2009/07 [Refereed][Not invited]
    Perylenediimide (PDI) dyes have attracted a great deal of attention as they possess excellent photochemical stability, high extinction coefficients, and fluorescence quantum yields. The use of multiple PDI chromophores in one synthetic architecture increases their versatile use and functionality even more. However, bringing multiple chromophores in close proximity also leads to interactions among the chromophores and opens up new photophysical pathways. Here, the synthesis and photophysical characterization, both at the ensemble and single molecule level, of a diphenyl-acetylene linked perylenediimide trimer (3PDIAc) is presented. Forster type energy transfer processes like energy hopping and singlet-singlet annihilation among the chromophores are investigated. Despite the lower singlet-singlet annihilation rate of the phenoxy substituted perylenediimide chromophores (356 ps) versus for example perylenemonoimide (10 ps), the system still behaves as a single photon emitter. Sequential fitting of the dipole emission pattern recorded with defocused wide field imaging of single 3PDIAc, immobilized in a PMMA polymer film, demonstrated that emission can switch between sequential emission of all of the chromophores or emission from one chromophore that likely is the lowest in energy.
  • Tai-Yang Kim, Hiroshi Uji-i, Martina Moeller, Benoit Muls, Johan Hofkens, Ulrike Alexiev
    BIOCHEMISTRY 48 (18) 3801 - 3803 0006-2960 2009/05 [Refereed][Not invited]
    Heterotrimeric G-proteins interact with their G-protein-coupled receptors (GPCRs) via key binding elements comprising the receptor-specific C-terminal segment of the alpha-subunit and the lipid anchors at the alpha-subunit N-terminus and the gamma-subunit C-terminus. Direct information about diffusion and interaction of GPCRs and their G-proteins is mandatory for all understanding of the signal transduction mechanism. By using single-particle tracking, we show that the encounters of the alpha-subunit C-terminus With the GPCR rhodopsin change after receptor activation. Slow as well as less restricted diffusion compared to the inactive state within domains 60-280 nm in length was found for the receptor-bound C-terminus, indicating short-range order in rhodopsin packing.
  • James A. Hutchison, Silvia P. Centeno, Hideho Odaka, Hiroshi Fukumura, Johan Hofkens, Hiroshi Uji-i
    NANO LETTERS 9 (3) 995 - 1001 1530-6984 2009/03 [Refereed][Not invited]
    We demonstrate that focused laser excitation at the end of silver nanowires of 50-150 nm diameter excites SERS hot-spots at points of nanoparticle adsorption many micrometers along the wire due to the plasmon waveguide effect. The total SERS Intensity detected at the hot-spots following wire-end excitation correlates with the known wavelength, polarization, and distance dependences of surface plasmon polariton (SPP) propagation in nanowires. The SERS spectra obtained at the hot-spots following wire-end excitation show very little background compared to when excitation occurs directly at the hot-spot, suggesting that a much smaller SERS excitation volume Is achieved by remote, waveguide excitation. The ability to transfer SERS excitation over several micrometers, through a structure with a subdiffraction limit diameter, Is discussed with respect to potential high-resolution SERS imaging applications.
  • Peter Dedecker, Benoit Muls, Ania Deres, Hiroshi Uji-i, Jun-ichi Hotta, Michel Sliwa, Jean-Philippe Soumillion, Klaus Muellen, Joerg Enderlein, Johan Hofkens
    ADVANCED MATERIALS 21 (10-11) 1079 - 1090 0935-9648 2009/03 [Refereed][Not invited]
    Today's miniature devices and biological systems share the fact that their dynamics and properties cannot be understood, in terms of macroscopic concepts, but require a thorough understanding of the nanoscale structuring This structuring is often very heterogeneous both in time and in space, and is difficult or impossible to resolve with traditional approaches. In this Progress Report, we will discuss how single-molecule microscopy - and defocused wide-field field imaging in particular-can be used to shed light on these phenomena.
  • Susana Rocha, James A. Hutchison, Kalina Peneva, Andreas Herrmann, Klaus Muellen, Michael Skjot, Christian I. Jorgensen, Allan Svendsen, Frans C. De Schryver, Johan Hofkens, Hiroshi Uji-i
    CHEMPHYSCHEM 10 (1) 151 - 161 1439-4235 2009/01 [Refereed][Not invited]
    Many of the biological processes taking place in cells are mediated by enzymatic reactions occurring in the cell membrane. Understanding interfacial enzymatic catalysis is therefore crucial to the understanding of cellular function. Unfortunately, a full picture of the overall mechanism of interfacial enzymatic catalysis, and particularly the important diffusion processes therein, remains unresolved. Herein we demonstrate that single-molecule wide-field fluorescence microscopy can yield important new information on these processes. We image phospholipase enzymes acting upon bilayers of their natural phospholipid substrate, tracking the diffusion of thousands of individual enzymes while simultaneously visualising local structural changes to the substrate layer. We study several enzyme types with different affinities and catalytic activities towards the substrate. Analysis of the trajectories of each enzyme type allows us successfully to correlate the mobility of phospholipase with its catalytic activity at the substrate. The methods introduced herein represent a promising new approach to the study of interfacial/heterogeneous catalysis systems.
  • Dominik Woll, Els Braeken, Ania Deres, Frans C. De Schryver, Hiroshi Uji-i, Johan Hofkens
    CHEMICAL SOCIETY REVIEWS 38 (2) 313 - 328 0306-0012 2009 [Refereed][Not invited]
    This tutorial review summarizes the most important results and developments in the field of polymer science by means of single molecule fluorescence spectroscopy (SMFS) at ambient temperatures. A broad range of topics will be addressed and it will be discussed which single molecule methods are suitable to get the maximum amount of information about polymer structure, polymer dynamics and the photophysics of incorporated or embedded dye molecules. In particular, we will report on the use of polymer films for immobilization of molecules, the visualization of dynamics near the glass transition temperature T-g, the reptation of polymer chains, the conformation adopted by polymer chains and the in situ observation of the polymerization reaction itself.
  • Chang Chen, James Andell Hutchison, Francesca Clemente, Ronald Kox, Hiroshi Uji-I, Johan Hofkens, Liesbet Lagae, Guido Maes, Gustaaf Borghs, Pol Van Dorpe
    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 48 (52) 9932 - 9935 1433-7851 2009 [Refereed][Not invited]
  • M. Linh Tran, Silvia P. Centeno, James A. Hutchison, Hans Engelkamp, Duoduo Liang, Gustaaf Van Tendeloo, Bert F. Sels, Johan Hofkens, Hiroshi Uji-i
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 130 (51) 17240 - + 0002-7863 2008/12 [Refereed][Not invited]
    A simple and low-cost method to create metal-metal hybrid nanostructures possessing fairly regularly spaced "hot-spots" of surface plasmon resonances is proposed. The nanohybrid structure was prepared via self-assembly during a simple drop-casting procedure, using chemically synthesized silver nanowires and silver nanoparticles prepared in a single batch of a polyol process. Wide field illumination of these nanohybrids produced hot-spots with spacings of around 500 nm to 1 mu m. The intensity of the emission/scattering from the hot-spots fluctuates over time. The proposed structure can be useful for the development of molecular-sensors or as a substrate for surface enhanced Raman/fluorescence spectroscopy.
  • Kazukuni Tahara, Shengbin Lei, Wael Mamdouh, Yui Yamaguchi, Tomoyuki Ichikawa, Hiroshi Uji-i, Motohiro Sonoda, Keiji Hirose, Frans C. De Schryver, Steven De Feyter, Yoshito Tobe
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 130 (21) 6666 - + 0002-7863 2008/05 [Refereed][Not invited]
    We present here the formation of a modular 2D molecular network composed of two different types of square-shaped butadiyne-bridged macrocycles, having intrinsic molecular voids, aligned alternately at the solid-liquid interface. Site-selective inclusion of a guest cation took place at every other molecular void in the molecular network with two different recognition sites.
  • Maarten B. J. Roeffaers, Rob Ameloot, Mukulesh Baruah, Hiroshi Uji-i, Metin Bulut, Gert De Cremer, Ulrich Mueller, Pierre A. Jacobs, Johan Hofkens, Bert F. Sels, Dirk E. De Vos
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 130 (17) 5763 - 5772 0002-7863 2008/04 [Refereed][Not invited]
    Understanding the internal structure of ZSM-5 crystallites is essential for improving catalyst performance. In this work, a combination of fluorescence microscopy, AFM, SEM, and optical observations is employed to study intergrowth phenomena and pore accessibility in a set of five ZSM-5 samples with different crystal morphologies. An amine-functionalized perylene dye is used to probe acid sites on the external crystal surface, while DAMPI (4-(4-diethylaminostyryl)-N-methylpyridinium iodide) is used to map access to the straight channels in MFI from the outer surface. The use of these dyes is validated by studying the well-understood rounded-boat type ZSM-5 crystals. Next coffin-shaped ZSM-5 crystals are considered; we critically evaluate the seemingly conflicting 2-component and 3-component models that have been proposed to account for the hourglass structure in these crystals. The data prove that observation of an hourglass structure is essentially unrelated to a 901 rotation of the pyramidal crystal components under the (010) face. Hence, in perfectly formed coffin-shaped crystals, the straight channels can be accessed from (010). However, in other crystal batches, sections with a 90 degrees rotation can be found; they are indeed located inside the crystal sections under (010) but often only partially occupy these pyramidal components. In such a case, both straight and sinusoidal pores surface at the hexagonal face. The results largely support the 3-component model, but with the added notion that 900 rotated sections (as proposed in the 2-component model) are most likely to be formed inside the defect-rich, pyramidal crystal sections under the (010) faces.
  • Jaesung Yang, Mira Park, Zin Seok Yoon, Takaaki Hori, Xiaobin Peng, Naoki Aratani, Peter Dedecker, Jun-ichi Hotta, Hiroshi Uji-i, Michel Sliwa, Johan Hofkens, Atsuhiro Osuka, Dongho Kim
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 130 (6) 1879 - 1884 0002-7863 2008/02 [Refereed][Not invited]
    By using single molecule fluorescence spectroscopy we have investigated the excitation energy migration processes occurring in a series of cyclic porphyrin arrays bearing a close proximity in overall architectures to the LH2 complexes in purple bacterial photosynthetic systems. We have revealed that the conformational heterogeneity induced by the structural flexibility in large cyclic porphyrin arrays, which provides the nonradiative deactivation channels as an energy sink or trap, reduces significantly the energy migration efficiency. Our study provides detailed information on the energy migration efficiency of the artificial light-harvesting arrays at the single molecule level, which will be a guideline for future applications in single molecular photonic devices in the solid state.
  • Nathalie Katsonis, Andrea Minoia, Tibor Kudernac, Toshiki Mutai, Hong Xu, Hiroshi Uji-i, Roberto Lazzaroni, Steven De Feyter, Ben L. Feringa
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 130 (2) 386 - + 0002-7863 2008/01 [Refereed][Not invited]
    Upon deposition of an achiral solution of diarylethene 1 on the achiral surface of graphite, a highly ordered monolayer with large homachiral domains is formed by self-assembly. Scanning tunneling micro ropy and molecolar dynamics show that the building blocks forming this monolayer are chiral dinners. We suggest that the mechanism of formation of these chiral dinners is first, surface-Induced atropoisomerism, which provides diarylethene 1 with a fixed helicity, and second, shape recognition between atropoisomers having similar helicites.
  • Dominik Woell, Hiroshi Uji-i, Tobias Schnitzler, Jun-ichi Hotta, Peter Dedecker, Andreas Herrmann, Frans C. De Schryver, Klaus Muellen, Johan Hofkens
    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 47 (4) 783 - 787 1433-7851 2008 [Refereed][Not invited]
  • Kalina Peneva, Gueorgui Mihov, Fabian Nolde, Susana Rocha, Jun-ichi Hotta, Kevin Braeckmans, Johan Hofkens, Hiroshi Uji-i, Andreas Herrmann, Klaus Muellen
    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 47 (18) 3372 - 3375 1433-7851 2008 [Refereed][Not invited]
  • Peter Dedecker, Jun-Ichi Hotta, Cristina Flors, Michel Sliwa, Hiroshi Uji-, Maarten B. J. Roeffaers, Ryoko Ando, Hideaki Mizuno, Atsushi Miyawaki, Johan Hofkens
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 129 (51) 16132 - 16141 0002-7863 2007/12 [Refereed][Not invited]
    The fast and reversible on/off switching of the fluorescence emission of the GFP-like fluorescent protein Dronpa has attracted considerable interest for applications in subdiffraction imaging. In this paper we study the use of a donut-mode beam in combination with two more overlapping laser beams to increase the imaging resolution through selective switching to the nonfluorescent photoswitched state. We devise and run a series of numerical simulations to determine suitable photophysical parameters of prospective, thermally stable photoswitchable molecules, in terms of photoswitching quantum yields, fatigue resistance, and possible presence of transient nonfluorescent states. Many of our findings are applicable to other measurements that make use of donut beams, and these guidelines can be used in the synthesis and screening of novel pholoswitchable compounds. We experimentally demonstrate the possibility of obtaining increased resolution by making use of the efficient and thermally stable Dronpa photoswitching, using equipment that is commonly available.
  • Cristina Flors, Jun-ichi Hotta, Hiroshi Uji-i, Peter Dedecker, Ryoko Ando, Hideaki Mizuno, Atsushi Miyawaki, Johan Hofkens
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 129 (45) 13970 - 13977 0002-7863 2007/11 [Refereed][Not invited]
    The photophysical properties and photoswitching scheme of the reversible photoswitchable green fluorescent protein-like fluorescent proteins Dronpa-2 and Dronpa-3 were investigated by means of ensemble and single-molecule fluorescence spectroscopy and compared to those of the precursor protein Dronpa. The faster response to light and the faster dark recovery of the new mutants observed in bulk also hold at the single-molecule level. Analysis of the single-molecule traces allows us to extract the efficiencies and rate constants of the pathways involved in the forward and backward switching, and we find important differences when comparing the mutants to Dronpa. We rationalize our results in terms of a higher conformational freedom of the chromophore in the protein environment provided by the P-can. This thorough understanding of the photophysical parameters has allowed us to optimize the acquisition parameters for camera-based sub-diffraction-limit imaging with these photochromic proteins. We show that Dronpa and its mutants are useful for fast photoactivation-localization microscopy (PALM) using common wide-field microscopy equipment, as individual fluorescent proteins can be localized several times. We provide a new approach to achieve fast PALM by introducing simultaneous two-color stroboscopic illumination.
  • Maarten B. J. Roeffaers, Gert De Cremer, Hiroshi Uji-i, Benlot Muls, Bert F. Sels, Pierre A. Jacobs, Frans C. De Schryver, Dirk E. De Vos, Johan Hofkens
    PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 104 (31) 12603 - 12609 0027-8424 2007/07 [Refereed][Not invited]
    The ever-improving time and space resolution and molecular detection sensitivity of fluorescence microscopy offer unique opportunities to deepen our insights into the function of chemical and biological catalysts. Because single-molecule microscopy allows for counting the turnover events one by one, one can map the distribution of the catalytic activities of different sites in solid heterogeneous catalysts, or one can study time-dependent activity fluctuations of individual sites in enzymes or chemical catalysts. By experimentally monitoring individuals rather than populations, the origin of complex behavior, e.g., in kinetics or in deactivation processes, can be successfully elucidated. Recent progress of temporal and spatial resolution in single-molecule fluorescence microscopy is discussed in light of its impact on catalytic assays. Key concepts are illustrated regarding the use of fluorescent reporters in catalytic reactions. Future challenges comprising the integration of other techniques, such as diffraction, scanning probe, or vibrational methods in single-molecule fluorescence spectroscopy are suggested.
  • Mira Park, Min-Chul Yoon, Zin Seok Yoon, Takaaki Hori, Xiaobin Peng, Naoki Aratani, Jun-ichi Hotta, Hiroshi Uji-i, Michel Sliwa, Johan Hofkens, Atsuhiro Osuka, Dongho Kim
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 129 (12) 3539 - 3544 0002-7863 2007/03 [Refereed][Not invited]
    Covalently linked cyclic porphyrin arrays have been synthesized to mimic natural light-harvesting apparatuses and to investigate the highly efficient energy migration processes occurring in these systems for future applications in molecular photonics. To avoid an ensemble-averaged picture, we performed a single-molecule spectroscopic study on the energy migration processes of cyclic porphyrin arrays and a linear model compound embedded in a rigid polymer matrix by recording fluorescence intensity trajectories, by performing coincidence measurements, and by doing wide-field defocused imaging. Our study demonstrates efficient energy migration within the cyclic porphyrin arrays at the single-molecule level. By comparison with the data of the linear model compound, we could pinpoint the role of the dipole-dipole coupling between diporphyrin subunits and the rigidity of the cyclic structures on the energy transfer processes.
  • Sergey M. Melnikov, Edwin K. L. Yeow, Hiroshi Uji-i, Mircea Cotlet, Klaus Muellen, Frans C. De Schryver, Joerg Enderlein, Johan Hofkens
    JOURNAL OF PHYSICAL CHEMISTRY B 111 (4) 708 - 719 1520-6106 2007/02 [Refereed][Not invited]
    Forster type resonance energy transfer (FRET) in donor-acceptor peryleneimide-terrylenediimide dendrimers has been examined at the single molecule level. Very efficient energy transfer between the donor and the acceptor prevent the detection of donor emission before photobleaching of the acceptor. Indeed, in solution, on exciting the donor, only acceptor emission is detected. However, at the single molecule level, an important fraction of the investigated individual molecules (about 10-15%) show simultaneous emission from both donor and acceptor chromophores. The effect becomes apparent mostly after photobleaching of the majority of donors. Single molecule photon flux correlation measurements in combination with computer simulations and a variety of excitation conditions were used to determine the contribution of an exciton blockade to this two-color emission. Two-color defocused wide-field imaging showed that the two-color emission goes hand in hand with an unfavorable orientation between one of the donors and the acceptor chromophore.
  • Xiaohong Cheng, An Ver Heyen, Wael Mamdouh, Hiroshi Uji-i, Frans De Schryver, Sigurd Hoeger, Steven De Feyter
    LANGMUIR 23 (3) 1281 - 1286 0743-7463 2007/01 [Refereed][Not invited]
    Shape-persistent macrocycles with interiors in the nanometer regime were prepared by the oxidative cyclization of the appropriate bisacetylene precursors under high-dilution conditions. These compounds contain polycyclic aromatic hydrocarbons in the ring backbone and are decorated with extra annular oligoalkyl or silyl side groups. Interestingly, after depositing them on different surfaces and investigating the self-assembled structures by means of scanning tunneling microscopy (STM) and atomic force microscopy (AFM), various nanostructures were observed. STM showed that these macrocycles are organized in two-dimensional (2D) layers, whereas AFM showed, in addition, the formation of 2D crystallites and one-dimensional fibrils. These results reveal the importance of the extra annular substitution of the macrocycles in creating patterned surfaces and nanoscale objects.
  • Maarten B. J. Roeffaers, Bert F. Sels, Hiroshi Uji-i, Bart Blanpain, Pieter L'hoest, Pierre A. Jacobs, Frans C. De Schryver, Johan Hofkens, Dirk E. De Vos
    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 46 (10) 1706 - 1709 1433-7851 2007 [Refereed][Not invited]
  • S. De Feyter, A. Miura, H. Uji-i, P. Jonkheijm, A. P. H. J. Schenning, E. W. Meijer, Z. Chen, F. Wuerthner, N. Schuurmans, J. van Esch, B. Feringa, F. C. De Schryver
    NANOSCIENCE AND TECHNOLOGY, PTS 1 AND 2 121-123 369 - 372 1012-0394 2007 [Refereed][Not invited]
    With scanning tunneling microscopy (STM), the intramolecular conformational and intermolecular ordering aspects have been investigated of a variety of organic molecules physisorbed at the liquid-solid interface. By balancing the interplay between intramolecular and intermolecular interactions (hydrogen bonding), leading to control of the molecular conformation, foldamers were created which order into well-defined two-dimensional crystals. The nature of the hydrogen bonding groups in conjugated oligomers leads to the formation of infinite stacks and cyclic multimers, expressing the chiral nature of the molecules.
  • Peter Dedecker, Cristina Flors, Jun-ichi Hotta, Hiroshi Uji-i, Johan Hofkens
    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 46 (44) 8330 - 8332 1433-7851 2007 [Refereed][Not invited]
  • Kazukuni Tahara, Shuhei Furukawa, Hiroshi Uji-i, Tsutomu Uchino, Tomoyuki Ichikawa, Jian Zhang, Wael Mamdouh, Motohiro Sonoda, Frans C. De Schryver, Steven De Feyter, Yoshito Tobe
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 128 (51) 16613 - 16625 0002-7863 2006/12 [Refereed][Not invited]
    The self-assembly of a series of hexadehydrotribenzo[12] annulene (DBA) derivatives has been scrutinized by scanning tunneling microscopy (STM) at the liquid-solid interface. First, the influence of core symmetry on the network structure was investigated by comparing the two-dimensional (2D) ordering of rhombic bisDBA 1a and triangular DBA 2a (Figure 1). BisDBA 1a forms a Kagome network upon physisorption from 1,2,4-trichlorobenzene (TCB) onto highly oriented pyrolytic graphite (HOPG). Under similar experimental conditions, DBA 2a shows the formation of a honeycomb network. The core symmetry and location of alkyl substituents determine the network structure. The most remarkable feature of the DBA networks is the interdigitation of the nonpolar alkyl chains: they connect the pi-conjugated cores and direct their orientation. As a result, 2D open networks with voids are formed. Second, the effect of alkyl chain length on the structure of DBA patterns was investigated. Upon increasing the length of the alkyl chains (DBAs 3c-e) a transition from honeycomb networks to linear networks was observed in TCB, an observation attributed to stronger molecule-substrate interactions. Third, the effect of solvent on the structure of the nonpolar DBA networks was investigated in four different solvents: TCB as a polar aromatic solvent, 1-phenyloctane as a solvent having both aromatic and aliphatic moieties, n-tetradecane as an aliphatic solvent, and octanoic acid as a polar alkylated solvent. The solvent dramatically changes the structure of the DBA networks. The solvent effects are discussed in terms of factors that influence the mobility of molecules at the liquid-solid interface such as solvation.
  • Josep Puigmarti-Luis, Andrea Minoia, Hiroshi Uji-i, Concepcio Rovira, Jerome Cornil, Steven De Feyter, Roberto Lazzaroni, David B. Amabilino
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 128 (39) 12602 - 12603 0002-7863 2006/10 [Refereed][Not invited]
  • Jun-ichi Hotta, Hiroshi Uji-i, Johan Hofkens
    OPTICS EXPRESS 14 (13) 6273 - 6278 1094-4087 2006/06 [Refereed][Not invited]
    We demonstrated the fabrication of a phase shaper for generating a 'doughnut mode' laser beam using a thin, circular polymer film on a substrate. The fabrication method is based on a combination of spin-coating and drop-casting. The alignment procedure to get ideal 'doughnut modes' is described. The intensity distribution at the focus is analyzed with single molecule spectroscopy. (c) 2006 Optical Society of America.
  • S Furukawa, H Uji-i, K Tahara, T Ichikawa, M Sonoda, FC De Schryver, Y Tobe, S De Feyter
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 128 (11) 3502 - 3503 0002-7863 2006/03 [Refereed][Not invited]
  • H Uji-i, SM Melnikov, A Deres, G Bergamini, F De Schryver, A Herrmann, K Mullen, J Enderlein, J Hofkens
    POLYMER 47 (7) 2511 - 2518 0032-3861 2006/03 [Refereed][Not invited]
    Defocused wide-field fluorescence microscopy was used to follow the 3D molecular rotational diffusion of a fluorescent probe molecule in a polymer thin film. The technique allows for visualizing the molecular reorientation both in-plane and out-of-plane. The local environmental change driven by heterogeneous dynamics of the polymer can be probed on a scale of I mu m as demonstrated by parallel imaging of several molecules. A multi-component rotational diffusion decay is observed which might reflect both different relaxation regimes of the polymer as well as rapid changes of the local environment. (c) 2006 Elsevier Ltd. All rights reserved.
  • MBJ Roeffaers, BF Sels, H Uji-i, FC De Schryver, PA Jacobs, DE De Vos, J Hofkens
    NATURE 439 (7076) 572 - 575 0028-0836 2006/02 [Refereed][Not invited]
    Catalytic processes on surfaces have long been studied by probing model reactions on single-crystal metal surfaces under high vacuum conditions. Yet the vast majority of industrial heterogeneous catalysis occurs at ambient or elevated pressures using complex materials with crystal faces, edges and defects differing in their catalytic activity. Clearly, if new or improved catalysts are to be rationally designed, we require quantitative correlations between surface features and catalytic activity - ideally obtained under realistic reaction conditions(1-3). Transmission electron microscopy(4-6) and scanning tunnelling microscopy(7,8) have allowed in situ characterization of catalyst surfaces with atomic resolution, but are limited by the need for low-pressure conditions and conductive surfaces, respectively. Sum frequency generation spectroscopy can identify vibrations of adsorbed reactants and products in both gaseous and condensed phases(9), but so far lacks sensitivity down to the single molecule level. Here we adapt real-time monitoring of the chemical transformation of individual organic molecules by fluorescence microscopy(10-12) to monitor reactions catalysed by crystals of a layered double hydroxide immersed in reagent solution. By using a wide field microscope, we are able to map the spatial distribution of catalytic activity over the entire crystal by counting single turnover events. We find that ester hydrolysis proceeds on the lateral {10 (1) over bar0} crystal faces, while transesterification occurs on the entire outer crystal surface. Because the method operates at ambient temperature and pressure and in a condensed phase, it can be applied to the growing number of liquid-phase industrial organic transformations to localize catalytic activity on and in inorganic solids. An exciting opportunity is the use of probe molecules with different size and functionality, which should provide insight into shape-selective or structure-sensitive catalysis(13-15) and thus help with the rational design of new or more productive heterogeneous catalysts.
  • W. Verheijen, H. Uji-i, C. Flors, J. Hotta, J. Hofkens
    The dynamical behavior of individual enzymes is studied by confocal microscopy. This technique makes it possible to gain insights into the detailed spectrum of molecular conformational changes and activities. We report the direct observation of a single CalB lipase-catalyzed reaction for extended periods of time (hours). A model in which a broad spectrum of conformations is involved is has to be invoked in order to explain the stretched exponential behavior of the off-times histograms.
  • H Uji-i, P Foubert, FC De Schryver, S De Feyter, E Gicquel, A Etoc, C Moucheron, A Kirsch-De Mesmaeker
    CHEMISTRY-A EUROPEAN JOURNAL 12 (3) 758 - 762 0947-6539 2006/01 [Refereed][Not invited]
    Topological modifications of plasmid DNA adsorbed on a variety of surfaces were investigated by using atomic force microscopy (AFM). On mica modified with 3-aminopropyltriethoxysilane (APS) or poly-L-lysine, the interaction between the plasmid DNA and the surface "freezes" the plasmid DNA conformation deposited from solution, and the AFM images resemble the projection of the three-dimensional conformation of the plasmid DNA in solution. Modified mica with low concentrations of Mg2+ leads to a decrease in the interaction strength between plasmid DNA and the substrate, and the AFM images reflect the relaxed or equilibrium conformation of the adsorbed plasmid DNA. Under these optimized deposition conditions, topological modifications of plasmid DNA were produced under irradiation in the presence of [Ru(TAP)(3)](2+) (TAP=1,4,5,8-tetraazaphenanthrene), which is a nonintercalating complex, and were followed as a function of illumination time. The observed structural changes correlate well with the conversion of the supercoiled covalently closed circular form (ccc form) into the open circular form (oc form), induced by a singlestrand photocleavage. The AFM results obtained after fine-tuning of the plasmid DNA-substrate interaction compare well with those observed from gel electrophoresis, indicating that under the appropriate deposition conditions, AFM is a reliable technique to investigate irradiation-induced topological changes in plasmid DNA.
  • S. De Feyter, H. Uji-i, W. Mamdouh, A. Miura, J. Zhang, P. Jonkheijm, A. P. H. J. Schenning, E. W. Meijer, Z. Chen, F. Wuerthner, N. Schuurmans, J. van Esch, B. L. Feringa, A. E. Dulcey, V. Percec, F. C. De Schryver
    INTERNATIONAL JOURNAL OF NANOTECHNOLOGY 3 (4) 462 - 479 1475-7435 2006 [Refereed][Not invited]
    The liquid/solid interface provides an ideal environment to investigate self-assembly phenomena, and scanning tunnelling microscopy (STM) is one of the preferred methodologies to probe the structure and the properties of physisorbed monolayers on the nanoscale. Physisorbed monolayers are of relevance in areas such as lubrication, patterning of surfaces on the nanoscale, and thin film based organic electronic devices, to name a few. It's important to gain insight in the factors which control the ordering of molecules at the liquid/solid interface in view of the targeted properties. STM provides detailed insight into the importance of molecule-substrate (epitaxy) and molecule-molecule interactions to direct the ordering of both achiral and chiral molecules on the atomically flat surface. The electronic properties of the self-assembled physisorbed molecules can be probed by taking advantage of the operation principle of STM, revealing spatially resolved intramolecular differences within these physisorbed molecules.
  • W Mamdouh, H Uji-i, JS Ladislaw, AE Dulcey, Percec, V, FC De Schryver, S De Feyter
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 128 (1) 317 - 325 0002-7863 2006/01 [Refereed][Not invited]
    The effect of solvent on the two-dimensional (2D) supramolecular ordering of monodendron 1 at the liquid-solid interface has been systematically investigated by means of scanning tunneling microscopy (STM). Solvents range from those with hydrophilic solvating properties, such as alkylated alcohols and acids, to hydrophobic solvents such as alkylated aromatics and alkanes. Dramatic differences in the 2D ordering are observed depending on the nature of the solvent. Of particular interest is the fact that in hydrophobic solvating solvents, such as aliphatic and aromatic hydrocarbons, solvent molecules are coadsorbed in the 2D molecular network while this is not the case for alkylated alcohols or acids. Furthermore, in the case of the coadsorbing solvents, a striking influence of the alkyl chain length has been observed on the 2D pattern formed. The solvent and alkyl chain length dependences are discussed in terms of molecule-molecule interactions (homo and hetero) and molecule-substrate interactions.
  • B Muls, H Uji-i, S Melnikov, A Moussa, W Verheijen, JP Soumillion, J Josemon, K Mullen, J Hofkens
    CHEMPHYSCHEM 6 (11) 2286 - 2294 1439-4235 2005/11 [Refereed][Not invited]
    Wide-field imaging of individual multichromophoric molecules and successive photobleaching were used to determine, accurately, the relative position of the chromophores in such systems. First, a polyphenylene dendrimer with well-defined geometry was used to establish the accuracy in localization that can be obtained by this methodology. For a signal-to-noise ratio of 20, interchromophoric distances could be measured with 4 nm accuracy. Next, the method was used to determine the end-to-end distribution of an end-capped polyfluorene polymer. From comparison between the experimental and simulated distributions, information on the conformation of the polymer could be deduced. It was found that the polymer has a nonlinear conformation. A conjugation length of six monomer units gave the best fit of the experimental data to the proposed model.
  • H Fukumura, D L-i, H Uji-i, S Nishio, H Sakai, A Ohuchi
    CHEMPHYSCHEM 6 (11) 2383 - 2388 1439-4235 2005/11 [Refereed][Not invited]
    The structures of self-assembled monolayers of dioctadecyl selenide (CH3(CH2)(17))(2)Se and dioctadecyl telluride (CH3(CH2)(17))(2)Te, as well as dioctadecyl ether (CH3(CH2)(17))(2)O and dioctadecyl sulfide (CH3(CH2)(17))(2)S, on graphite at the liquid-solid interface were systematically investigated by scanning tunneling microscopy (STM). Both dioctadecyl selenide and telluride formed monolayer structures in which the tilt angle between the molecular axis of the alkyl chain and the lamellae axis was 90 degrees, while dioctadecyl ether assembled with a tilt angle of 60 degrees. Dioctadecyl sulfide was found to make two different self-assembled structures having tilt angles of 60 and 90 degrees. When selenide was embedded in ether compounds in mixed self-assembled monolayers, the alkyl chains of the selenide become blurred, implying that the alkyl chains in the monolayers were unstable. This is in contrast with the structure of co-adsorbed monolayers of the ether and sulfide compounds, where the images of all alkyl chains hod high spatial resolution. For the co-adsorbed monolayers, the image contrast of chalcogen atoms was normalized compared with that of alkyl chains of the ether compound in the some image frame. The normalized image contrast was found to be independent of the measurement conditions involving tip shapes, having the following trend, Te > Se > S > C > O. The difference in the normalized image contrast among chalcogen atoms are discussed based on fundamental parameters like polarizability and atomic radii.
  • MMS Abdel-Mottaleb, E Gomar-Nadal, M Surin, H Uji-i, W Mamdouh, J Veciana, Lemaur, V, C Rovira, J Cornil, R Lazzaroni, DB Amabilino, S De Feyter, FC De Schryver
    JOURNAL OF MATERIALS CHEMISTRY 15 (43) 4601 - 4615 0959-9428 2005/11 [Refereed][Not invited]
    The self-assembly of a series of tetrathiafulvalene (TTF) derivatives at the interface between non-volatile organic solutions and the graphite surface has been studied by scanning tunnelling microscopy (STM). The TTFs have been prepared such that they bear none, one, two (in different constitutions) or four alkyl chains of different lengths and different functional groups. The STM images reveal that the packing of the TTF cores can effectively be controlled by changing the substitution pattern on the heterocycle. Several structures are seen at the interphase - parquet-type packing, single and double core tapes, and even isolated molecules - all of which have the TTF core essentially coplanar with the surface. Molecular modelling has shown that several orientations of the molecules are practically equal in energy on the graphite, which explains the polymorphous packing of some of the molecules. Solvent effects also play a role in determining the 2D structures.
  • H Uji-i, A Miura, A Schenning, EW Meijer, ZJ Chen, F Wurthner, FC De Schryver, M Van der Auweraer, S De Feyter
    CHEMPHYSCHEM 6 (11) 2389 - 2395 1439-4235 2005/11 [Refereed][Not invited]
    By means of scanning tunneling microscopy (STM), the self-assembly of two organic donor-acceptor-donor triads (donor=oligo(p-phenylene vinylene) (OPV); acceptor=perylene diimide (PDI)) and their mixtures has been investigated at the liquid/solid interface, Both triads differ in the nature of the substituents and, therefore, in the redox properties of the central perylene diimide unit (H or Cl). Thanks to the submolecular resolution, the distinct electronic properties of the units, within a triad and between the two triads, are reflected by the relative STM contrast in the bias-dependent imaging experiments. Moreover, scanning tunneling spectroscopy reveals an inverse rectifying behavior of the OPV and H-substituted PDI units, which is discussed in the framework of quasi-resonant tunneling. A striking difference is observed for the Cl-substituted triad.
  • S Nishio, D I-i, H Matsuda, M Yoshidome, H Uji-i, H Fukumura
    A nanospace polymerization reaction was initiated using a scanning tunneling microscope in a monolayer of a diacetylene derivative, 10, 12-nonacosadiynoic acid (NCDA), at a solid-liquid interface to obtain molecular wires. The polymerization threshold with respect to the applied voltage was 2 V, which was I V lower than that observed at a solid-air interface. The presence of ionic species considerably enhanced the reaction probability. At more than 2 V, the addition of N(CH(3))(4)ClO(4) resulted in the expansion of the reaction region and the increase in reaction probability regardless of the sign of the bias voltage applied. Different from the case at the solid-air interface, polymerization at the solid-liquid interface was probably induced through the multiple vibrational excitation of NCDA by repetitive collisions with charged carriers activated by the strong electric field involved in electron avalanche.
  • H Uji-i, S Nishio, H Fukumura
    CHEMICAL PHYSICS LETTERS 408 (1-3) 112 - 117 0009-2614 2005/06 [Refereed][Not invited]
    Two kinds of self-assembled structures of 1-pyrenehexadecanoic acid at a solution-graphite interface were investigated using scanning tunneling microscopy. The pyrenyl groups of 1-pyrenehexadecanoic acid formed a pi-stacked assembly when it was co-adsorbed with 4,4'-dipyridyl although the pyrenyl groups remained isolated in the one-component self-assembled structure. On the basis of the Davidov splitting model, the shift of the pyrenyl group's electronic levels, upon formation of the pi-stacked assembly, was estimated from the observed structures. The energy shift was found to be consistent with the observed change in the electron-tunneling spectra between these two different structures. (c) 2005 Elsevier B.V. All rights reserved.
  • APHJ Schenning, P Jonkheijm, FJM Hoeben, J van Herrikhuyzen, SCJ Meskers, EW Meijer, LM Herz, C Daniel, C Silva, RT Phillips, RH Friend, D Beljonne, A Miura, S De Feyter, M Zdanowska, H Uji-i, FC De Schryver, Z Chen, F Wurthner, M Mas-Torrent, D den Boer, M Durkut, P Hadley
    SYNTHETIC METALS 147 (1-3) 43 - 48 0379-6779 2004/12 [Refereed][Not invited]
    We have demonstrated that it is possible to program pi-conjugated molecules to self-assemble into cylindrical aggregates in solution. By incorporating energy or electron traps in our stacks, energy and electron transfer processes in these one-dimensional assemblies have been studied in solution. The transfer of the single OPV cylinders from solution to a solid support as isolated objects was only possible when specific concentrations and specific solid supports were used. So far, however, we have not been able to measure any current through our fibers. (C) 2004 Elsevier B.V All rights reserved.
  • S Nishio, M Yoshidome, H Uji-i, J Hobley, H Fukumura, KA Zachariasse
    CHEMISTRY LETTERS 33 (11) 1506 - 1507 0366-7022 2004/11 [Refereed][Not invited]
    N,N-Dimethyl-p-[15-(1-pyrenyl)pentadecanyt]aniline (Py15DMA); 15-(p-N,N-dimethylaminophenyl)pentadecanylpyrene-1-carboxylate (Py(COO)16 DMA); and 1,16-di(1-pyrene)hexadecane (Py16Py) monolayers sorbed at a liquid-solid interface were probed using an STM. High definition images were obtained of sufficient quality to determine the structural parameters of the monolayers.
  • N Schuurmans, H Uji-i, W Mamdouh, FC De Schryver, BL Feringa, J van Esch, S De Feyter
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 126 (43) 13884 - 13885 0002-7863 2004/11 [Refereed][Not invited]
  • W Mamdouh, H Uji-i, A Gesquiere, S De Feyter, DB Amabilino, MMS Abdel-Mottaleb, J Veciana, FC De Schryver
    LANGMUIR 20 (22) 9628 - 9635 0743-7463 2004/10 [Refereed][Not invited]
    The effect that molecular chirality has on the formation of monolayer structures by pure enantiomers and their racemates at the liquid/solid interface has been investigated for two chiral compounds (1 and 2) which differ from each other by the presence or absence of an ester function in their respective molecular structures. 1 shows pseudoracemate formation when the achiral graphite support is exposed to a solution containing a racemate while 2 shows racemic conglomerate formation. This difference is rationalized in terms of the orientation of the pure enantiomers with respect to the graphite substrate and highlights the importance of molecular structure and its influence on balancing the interplay between molecular conformation and molecular packing on the surface. For 1, nonstoichiometric mixtures of both enantiomers have been investigated, and the results are discussed in the framework of the sergeant and soldiers principle. These results are important for the understanding and prediction of spontaneous resolution in monolayer systems.
  • W Mamdouh, H Uji-i, AE Dulcey, Percec, V, S De Feyter, FC De Schryver
    LANGMUIR 20 (18) 7678 - 7685 0743-7463 2004/08 [Refereed][Not invited]
    We have investigated the two-dimensional ordering of chiral and achiral monodendrons at the liquid-solid interface. The chiral molecules self-assemble into extended arrays of dimers. As expected, the R enantiomer forms the mirror image type pattern of the chiral two-dimensional structure formed by the S enantiomer. A racemic mixture applied from solution onto the substrate undergoes spontaneous segregation: the enantiomers separate on the surface and appear in different domains. In contrast to the chiral molecules, the achiral analogue self-assembles into cyclic tetramers. Moreover, the pattern formed by the achiral molecule strongly depends on the solvent used. In the case of 1-phenyloctane, solvent molecules are coadsorbed in a 2:1 (dendron:solvent) ratio whereas in I-octanol, no solvent molecules are coadsorbed. By the appropriate solvent choice, the distance between the potential "supramolecular containers" can be influenced.
  • A Miura, ZJ Chen, H Uji-i, S De Feyter, M Zdanowska, P Jonkheijm, APHJ Schenning, EW Meijer, F Wurthner, FC De Schryver
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 125 (49) 14968 - 14969 0002-7863 2003/12 [Refereed][Not invited]
  • H Uji-i, K Hatanaka, J Hobley, H Fukumura
    APPLIED PHYSICS LETTERS 79 (16) 2660 - 2662 0003-6951 2001/10 [Refereed][Not invited]
    A nanometer-scale surface modification of tin-doped indium oxide (ITO) in organic solvent was performed using a scanning tunneling microscope (STM). The surface modification was attributed to localized field evaporation upon applying 10 V between the tunneling gap. White light sparking beneath the STM tip (nanospark) was observed during and after the surface modification. The addition of ionic species into the otherwise pure solvent also induced a nanospark even when applying lower voltages, but in this case, surface modification did not occur. Thus, it is proposed that a part of the ITO becomes dissolved in solution as ions, which results in electron avalanche in the presence of these induced ions. (C) 2001 American Institute of Physics.
  • Sub-micrometer photochromic patterns using laser induced molecular implantation techniques (LIMIT)
    J Hobley, M Goto, M Kishimoto, H Fukumura, H Uji-I, M Irie
    MOLECULAR CRYSTALS AND LIQUID CRYSTALS 345 623 - + 1058-725X 2000 [Refereed][Not invited]
    LIMIT is a new approach for creating highly space selective patterns of molecules in thin polymer films. photochromic implants of <800 nm dimensions are now possible using interference modulated implantation. In this way implanted diffraction gratings have been made which operate as photo-switching optical devices. Here we report the implantation of four different classes of organic photochromic molecule.
  • A knowledge structure visualization for supporting exploratory learning in hyperspace
    A Kashihara, H Uji'i, J Toyoda
    ARTIFICIAL INTELLIGENCE IN EDUCATION 50 714 - 716 0922-6389 1999 [Refereed][Not invited]
    This paper discusses how to help learners reflect on what they have explored domain concepts/knowledge in hyperspace. The approach presented here is to visualize a knowledge structure that the learners would construct in exploring, In this paper, we address the following important problems to be resolved towards the knowledge structure visualization: (1) how to get learners' exploration processes, (2) how to help the learners keep and achieve exploration in hyperspace, and (3) how to visualize the knowledge structure understandably.
  • H Fukumura, H Uji-i, H Banjo, H Masuhara, DM Karnakis, N Ichinose, S Kawanishi, K Uchida, M Irie
    APPLIED SURFACE SCIENCE 127 761 - 766 0169-4332 1998/05 [Refereed][Not invited]
    Laser molecular implantation enables us to dope space-selectively a surface layer of a polymer film with intact organic molecules. Thus it is applicable towards building various kinds of devices utilizing functional organic molecules. This paper presents that photochromic molecules can be implanted in polymer surfaces by using 351 nm or 355 nm nanosecond lasers and the implanted molecules can be switched repetitively by the alternate irradiation of UV and visible lights. As an example of the space selectivity, the fabrication of gratings by laser implantation is demonstrated and evaluated from an application view point. (C) 1998 Elsevier Science B.V.


  • プラズモン導波路を用いた単一細胞解析と操作
    豊内秀一, 猪瀬朋子, 平井健二, 雲林院宏  月間「細胞」2020年 2月号  51  -54  2020  [Not refereed][Not invited]
  • 貴金属ナノワイヤが拓く新しい超解像顕微分光法
    藤田康彦, 猪瀬朋子, 雲林院宏  光化学  48-  (1)  2  -9  2017  [Refereed][Not invited]
  • 猪瀬朋子, 藤田康彦, 雲林院宏  生物物理  56-  (6)  327  -329  2016  [Refereed][Not invited]
  • Plasmonic waveguide endoscopy
    Hiroshi Ujii  ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY  247-  2014/03  [Not refereed][Not invited]
  • New insight into molecular recognition: Coupling of single G-proteins to active rhodopsin
    Ulrike Alexiev, Martina Moeller, Tai-Yang Kim, Kathrin Winkler, Hiroshi Ujii, Benoit Muls, Johan Hofkens  BIOPHYSICAL JOURNAL  187A  -187A  2007/01  [Not refereed][Not invited]
  • H Uji, M Yoshidome, J Hobley, K Hatanaka, H Fukumura  PHYSICAL CHEMISTRY CHEMICAL PHYSICS  5-  (19)  4231  -4235  2003/10  [Not refereed][Not invited]
    Static and dynamic structures in self-assembled monolayers containing 1-pyrenehexadecanoic acid (PHDA) at a liquid-solid interface were investigated with scanning tunneling microscopy. Uni-component adsorption layers made a specific structure having ring figures corresponding to pyrene groups, whereas the co-adsorption of PHDA and 4,4'-bipyridyl resulted in two different structures depending on their concentrations and the ambient temperature. When the concentration of 4,4'-bipyridyl was high and the temperature at around 290 K, a dynamic bistable structure was observed within a stacked row of molecules without causing any disorder to the assembly as a whole. The bistability is considered to be due to molecular desorption-adsorption process occurring at the anti-parallel configuration of two neighbouring PHDA molecules.

Educational Activities

Teaching Experience

  • Inter-Graduate School Classes(General Subject):Natural and Applied Sciences
    開講年度 : 2018
    課程区分 : 修士課程
    開講学部 : 大学院共通科目
    キーワード : ナノ構造、微細加工、光機能性材料、光化学、液晶、分子性物質、導電性、磁性、薄膜、電子顕微鏡、走査型プローブ顕微鏡、ナノワイヤー、二次元電子ガス、物性理論
  • Nanomaterials
    開講年度 : 2018
    課程区分 : 修士課程
    開講学部 : 情報科学研究科
    キーワード : ナノ材料、ナノテクノロジー、光物理、光科学、バイオテクノロジー
  • Inter-Graduate School Classes(General Subject):Natural and Applied Sciences
    開講年度 : 2018
    課程区分 : 修士課程
    開講学部 : 大学院共通科目
  • Nanomaterials
    開講年度 : 2018
    課程区分 : 博士後期課程
    開講学部 : 情報科学研究科
    キーワード : ナノ材料、ナノテクノロジー、光物理、光科学、バイオテクノロジー
  • Applied Materials Science
    開講年度 : 2018
    課程区分 : 学士課程
    開講学部 : 工学部
    キーワード : 固体、結晶、導電体、半導体

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