Hidenobu Nakao

Nano-scale imaging of chromosomes and DNA by scanning near-field optical/atomic force microscopy

Nano-scale structures of the YOYO-1-stained barley chromosomes and lambda-phage DNA were investigated by scanning near-field optical/atomic force microscopy (SNOM/AFM). This technique enabled precise analysis of fluorescence structural images in relation to the morphology of the biomaterials. The results suggested that the fluorescence intensity does not always correspond to topographic height of the chromosomes, but roughly reflects the local amount and/or density of DNA. Various sizes of the bright fluorescence spots were clearly observed in fluorescence banding-treated chromosomes. Furthermore, fluorescence-stained lambda-phage DNA analysis by SNOM/AFM demonstrated the possibility of nanometer-scale imaging for a novel technique termed nano-fluorescence in situ hybridization (nano-FISH). Thus, SNOM/AFM is a powerful tool for analyzing the structure and the function of biomaterials with higher resolution than conventional optical microscopes.

One-step preparation of positively-charged gold nanoraspberry

Self-assembling particles were prepared by a new synthetic strategy for a raspberry-like aggregate, based on three-dimensional particle-aniline oligomer-particle repeated sequences; this one-step process, without the need for extra control, organic solvents, or ligand exchange, could further help in the realization of nanoscale electronics and molecular devices.

Three-dimensional microfabrication using local electrophoresis deposition and a laser trapping technique

We describe a novel fabrication method of three-dimensional (3D) microstructures using local electrophoresis deposition together with laser trapping. A liquid cell consisting of two-faced conductive substrates was filled with a colloidal solution of Au nanoparticles. The nanoparticles were trapped by a laser spot and positioned on the bottom substrate, then deposited onto the surface by the application of electrical voltage between the two substrates. By moving the liquid cell downward while maintaining the deposition, 3D microstructures were successfully fabricated. The smallest diameter of the fabricated pillar was 500 nm, almost the same as that of the Airy disc. The Youngs modulus of the fabricated structure was 1.5 GPa.

Polyaniline–Poly(vinyl alcohol) Dispersions for Controlled Ion Exchange of Organic Sulfonates

The authors prepared colloidal dispersions consisting of polyaniline, dopant (perchlorate, benzenesulfonate or polystyrene sulfonate) and surfactant stabiliser [poly(vinyl alcohol)]. The dispersions took up anionic analytes in their oxidised forms and ejected the anions on deprotonation or reduction. Thus, uptake and release were controlled externally by varying the redox potential and/or pH in solution. Organic anions such as chromotropic acid anion and anthraquinone sulfonates were taken up quantitatively into the oxidised dispersion particles and concentrated 250–1000 times. Although the uptake of these anions was quantitative, ejection from the deprotonated or reduced forms was not so. In order to achieve high ejection efficiency, we prepared a dispersion of doping polystyrene sulfonate to introduce immobile negative charge. As a result, the recovery of chromotropic acid increased up to 100% at the cost of uptake capacity. Competitive interactions of the negative charge and targeted anion with the cationic sites in polyaniline were confirmed by electrochemical and electron spin resonance measurements and were responsible for the increase in the recovery. Electrochemical ejection of chromotropic acid was found to be quantitative when methyl viologen was present in solution as an electron mediator.

Local electrophoresis deposition of nanomaterials assisted by a laser trapping technique

We describe a novel local deposition technique for nanoparticles using electrophoresis deposition assisted by laser trapping. A solution containing nanometer scale colloidal Au particles was placed between a conductive substrate and a cover glass coated with an indium thin oxide film. Laser spots focused on the substrate gathered the nanoparticles around the spots, and the nanoparticles were then deposited on the substrate by controlling the electric potential between the substrate and the cover glass. A dots array and line patterning of the deposited Au nanoparticles were successfully demonstrated. Furthermore, by using a solution containing colloidal DNA, we were able to obtain a dots array of the DNA. This technique will be very useful for applications in micro-and nanodevices.

Fluorescence Enhancement of Nanoraspberry Hot-spot Source Composed of Gold Nanoparticles and Aniline Oligomers

In this study, we examined raspberry-shaped organic/inorganic hybrid structure for potential development of a nanoantenna system capable of detecting and labeling biomolecules. The structure is characterized by a high density of gold nanoparticles (AuNPs) separated by closely packed aniline oligomers that serve as a linkage between adjacent particles. In particular, the structure was based on repeated sequences of AuNP-aniline oligomer-AuNP in a three-dimensional arrangement, which enabled the creation of optical hot spots that can hold multiple molecules. We examine the expression of such features by focusing on the structure and characteristics of the hybrid. We demonstrate that these optical hot spots enhance the dye fluorescence without quenching. As a result, we were able to create a nanoantenna structure enabling the efficient use of light.

Enhanced collective optical response of vast numbers of silver nanoparticles assembled on a microbead

We investigated the optical response of a huge number of silver nanoparticles (AgNPs) densely assembled on an organic microsphere, i.e., AgNP-fixed bead, under the collective phenomena of localized surface plasmons. For this purpose, various optical properties of such a AgNP-fixed bead were analyzed in aqueous solution by dark-field optical microscopy and laser Raman microscopy. In particular, in comparison with the optical spectrum of single AgNPs, significant spectral broadening and redshift were observed due to plasmonic superradiance with decreasing interparticle distance to the subnanoscale when using small binder molecules in the AgNP-fixed bead. Furthermore, we observed surface-enhanced Raman scattering and clarified the sensitivity of the signal intensity to the size of the binder molecules between the AgNPs, which can be explained based on optical response theory using a discrete integral with spherical cells. These results and discussion provide a guiding principle for broadband plasmonic light absorbers and for highly sensitive detection of small molecules and nanoscale biomaterials based on vast numbers of nanogaps produced by a bottom-up self-assembly process.

Oxidative Polymerization Behavior of Diphenylamine with Bridged Structure

For convenient synthesis of polydiphenylamine with a bridged structure, oxidative polymerizations of diphenylamine with a bridged structure were carried out. Polymer was obtained when dibenzazepine (Azep) was used as a monomer, but oxidative polymerization of phenothiazine (Phen) did not afford polymer. Therefore, oxidation behavior of Phen was examined. From the result, it was suggested that oxidation of Phen affords S-oxide-type compound rather than formation of polydiphenylamine-type polymer.

Preparation and Properties of Poly(phenazasiline) with Various Substituents

Poly(phenazasiline) (PPhenaz) with various substituents was prepared, and the substituent effect was discussed. PPhenaz was prepared by dehalogenative polycondensation of the corresponding dibromophenazasiline (Phenaz). The conductivity of an electrochemically doped PPhenaz film was 10-1–101 S cm-1. Using PPhenaz as a hole-transporting layer, a double layer electroluminescent (EL) device was fabricated. The properties of the EL device improved, when the substituent of PPhenaz was small. We also fabricated organic thin-film transistors (OTFTs) using PPhenaz films. The transistors showed p-type properties. The conductivity and the transistor properties were not dependent on the density of phenazasiline in PPhenaz, whereas the properties of PPhenaz-containing EL devices depended on the size of the substituent in PPhenaz.

Analysis and simulation of optical response of Au-nanoparticle-fixed beads for optical sensors of microscopic local environment

Large red-shift of LSP resonance has been experimentally observed in a high density AuNP fixed bead fabricated by self-assembling technique. We also theoretically clarified the sensitivity of LSP spectra to the density of NPs on a bead. If we use the flexible organic material as a bead, the change of the bead diameter can induce the large shift of LSP resonance. This mechanism would be used for the sensor of temperature and pressure in the local environment corresponding to the size of AuNP-fixed beads.