Hiroshi Uji-i

KU Leuven | ku leuven · Department of Chemistry

Mapping the spatial and temporal heterogeneities in miscible polymer blends is critical for understanding and further improving their material properties. However, a complete picture on the heterogeneous dynamics is often obscured in ensemble measurements. Herein, the spatial and temporal heterogeneities in fully miscible polystyrene/oligostyrene b...

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 u...

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...

In this work, 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-promoted photochemical etching of silver in the presence of certain Raman probes, resulting in a dramatic...

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 th...

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 monolay...

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 H...

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 n...

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 ov...

In this work, hemicyanine dye LDS 722 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 20 μm×30 μm) suitabl...

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.,...

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 an...

Dans le domaine moléculaire, Les chercheurs étudient la dynamique des polymères par microscopie : différentes mesures telle que longueur et courbure sont calculées. Pour que ces mesures soient correctes, ils ont besoin d'extraire la courbe représentant au mieux la forme du polymère. A l'acquisition, le polymère se présente comme une courbe épaisse...

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...

Site-specific cutting of chemically synthesized silver nanowires is demonstrated by simple focusing of a femtosecond laser. Structure and separation length of the cut-ends can be controlled with sub-micrometer resolution. Plasmonic wave-guiding effect is conserved on the cut-wires. This demonstrates that the method can be potentially useful for dev...

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 nanosc...

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)...

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....

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 monit...

The ability to confine and direct light propagation at the surface of metals via surface plasmon polaritons has been at the centre of the growth in interest in nanoscale engineering of noble metals over the past decades. This chapter reviews the recent development in our laboratories of novel techniques for remote Raman and fluorescence sensing usi...

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. Towards a complete understanding of the complicated polymer dynamics in crowded...

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-r...

π-π intermolecular interactions among adjacent conjugated azobenzene 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 bi-stability for its optimal integration as respon...

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 sub...

Supplementary information available for this article at http://www.nature.com/ncomms/2015/150217/ncomms7287/suppinfo/ncomms7287_S1.html

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...

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 commonly used stabilizing agent CTABr in the etching process is explored, showing how it acts both as a so...

Changing abruptly the potential between a scanning tunneling microscope (STM) tip and a graphite substrate induces "high-conductance" spots at the molecular level in a monolayer formed by a manganese chloride porphyrin molecule (Mn(III)-PP). These events are attributed to the pulse-induced formation of μ-oxo porphyrin dimers. The pulse voltage must...

Dealuminated zeolites are widely used acid catalysts in research and 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 catalysts design still requires insight in t...

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 o...

Live-cell surface-enhanced Raman spectroscopy (SERS) endoscopy is developed by using plasmonic nanowire waveguides as endoscopic probes. It is demonstrated that the probe insertion does not stress the cell. Opposed to conventional SERS endoscopy, with excitation at the hotspot within the cell, the remote excitation method yields low-background SERS...

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.

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...

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 fluoresce...

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 track...

The epidermal growth factor (EGF) receptor transduces the extracellular EGF signal into the cells. The distribution of these EGF receptors in the plasma membrane is heterogeneous and dynamic, which is proposed to be important for the regulation of cell signaling. The response of the cells to a physiological concentration of EGF is not homogeneous,...

Developing molecular systems with functions analogous to those of macroscopic machine components, such as rotors, gyroscopes and valves, 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. In some instances, ratchet mechanis...

In the last two decades, fluorescent proteins became an indispensable tool to noninvasively label a protein in living cells. The discovery of photoswitchable fluorescent proteins expanded the applications of the fluorescent proteins to techniques such as molecular tracking and highlighting on a microscope. Recently, a new microscopic modality to ac...

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 mi...

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, an...

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 gene...

First published as an Advance Article on the web 5th September 2003 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 py...

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-electr...

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 silv...

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...

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...

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.

Screening photoactivatable fluorescent proteins (PAFP) for HIV-1 Gag labeling and PALM. (A) Constructs used for PALM: HIV-1 Gag consisting of matrix (MA), capsid (CA), nucleocapsid (NC) and p6 was fused to different photoactivatable proteins, namely Dronpa, PS-CFP2, Dendra2, mKikGR, mEosFP and PAmCherry. Color code refers to standard emission color...

Setup and excitation/detection scheme used for super-resolution microscopy. Setup, excitation and detection scheme used to measure Dronpa and Alexa Fluor 647 (A) or mEosFP and Alexa Fluor 647 fluorescence (B). Specific dicroic mirrors (DM1-4) and filters (BP1-2) are described in Material and Methods. OAM: acoustic optic modulator, MS1: mechanical s...

Incorporation of PAFP into HIV-1 virions and size histograms. A) Immunofluorescence analysis (anti-CA, red) of HIV-1 virions containing indicated PAFP (green), scale bar 1 µm. B) Size distribution of Dronpa-Vpr, Gag-Dronpa and Gag-mEosFP in HIV-1 virions from super-resolution imaging and cluster analysis. C) Size distribution of integrase (IN), cap...

Characterisation of tetherin mutants. (A) 293T cells were transfected with HIV-1 Δvpu and either tetherin-HA, tetherin-HA delTM or tetherin-HA delGPI without or with Vpu as indicated and infectious output was determined on HeLa indicator cells. Error bars represent range of duplicate titrations. (B) Western blot analysis of cell lysates from A) was...

Single molecule photo-physical characterization of mEosFP. (A) SDS-PAGE and Coomassie staining of 1 or 4 µg of purified 6xHis-tagged mEosFP. Sizes of molecular weight markers are shown in kilodaltons. The predicted size of 6xHis mEosFP is 31 kDa and lower molecular weight bands represent mEosFP cleavage products associated with premature photoactiv...

Colocalization procedure for two-color super-resolution microscopy. 100 nm fluorescent beads were used as fiducial markers to correct differences in alignment and chromatic aberrations of detection paths (A,B). Fields of 150–500 beads were imaged simultaneously in Dronpa channel (green) and Alexa Fluor 647 channel (red) and representative part of 2...

Calibration of cluster size analysis. (A) Examples of simulated fields of 25 circular cluster of different sizes containing 100 random localizations, scale bar 1 µm, (B) Ripley's L analysis of simulated clusters: Note decrease of peaks and shift of maxima towards larger r at larger cluster sizes, (C) Sizes of simulated clusters were estimated using...

Single molecule defocused wide-field fluorescence microscopy (SMDWM) has been used to monitor the 3D reorientation of single molecules in a thin polymer film (300 nm) of monodisperse poly(n-butyl methacrylate) near the glass temperature (Tg). Stroboscopic illumination allows for estimating reliable correlation times of single molecule rotational di...

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 immuno...

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 demon...

Polymer relaxation dynamics are complex processes. While polymers look homogeneous, they are in fact temporally and spatially heterogeneous at molecular level. Single-molecule spectroscopy (SMS) is an ideal tool to address such heterogeneity. This contribution will introduce the use of SMS to study the relaxation dynamics of polymers near the glass...

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 e...

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 si...

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 heteroge...

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 absorp...