Sunao Yamada

Rapid synthesis of gold nanorods by the combination of chemical reduction and photoirradiation processes; morphological changes depending on the growing processes

Combination of chemical reduction of tetrachloroaurate by ascorbic acid and subsequent ultraviolet photoirradiation resulted in the quick generation of gold nanorods quantitatively, with appreciable shape changes as the reaction proceeds.

Controlled release of plasmid DNA from gold nanorods induced by pulsed near-infrared light

Pulsed near-infrared laser irradiation induced release of plasmid DNA immobilized on gold nanorods without structural degradation, by selective excitation of longitudinal plasmon oscillation.

Photothermal reshaping of gold nanorods prevents further cell death

The combined use of phosphatidylcholine passivated gold nanorods (PC-NRs) and pulsed near-infrared (near-IR) irradiation resulted in cell death. Pulsed near-IR laser irradiation also induced reshaping of PC-NRs into spherical nanoparticles. Since reshaped particles showed no absorption in the near-IR region, successive laser irradiation did not affect cells. Photo-reshaping of PC-NRs is expected to be advantageous in preventing unwanted cell damage following destruction of target cells.

Plasmon-Enhanced Photocurrent Generation from Self-Assembled Monolayers of Phthalocyanine by Using Gold Nanoparticle Films

The effect of localized electric fields on the photocurrent responses of phthalocyanine that was self-assembled on a gold nanoparticle film was investigated by comparing the conventional and the total internal reflection (TIR) experimental systems. In the case of photocurrent measurements, self-assembled monolayers (SAMs) of a thiol derivative of palladium phthalocyanine (PdPc) were prepared on the surface of gold-nanoparticle film that was fixed on the surface of indium-tin-oxide (ITO) substrate via a polyion (PdPc/AuP/polyion/ITO) or on the ITO surface (PdPc/ITO). Photocurrent action spectra from the two samples were compared by using the conventional spectrometer, and were found that PdPc/AuP/polyion/ITO gave considerably larger photocurrent signals than PdPc/ITO under the identical concentration of PdPc. In the case of the TIR experiments for the PdPc/AuP/polyion/ITO and the PdPc/AuP/Glass systems, incident-angle profiles of photocurrent and emission signals were correlated with each other, and they were different from that of the PdPc/ITO system. Accordingly, it was demonstrated that the photocurrent signals were certainly enhanced by the localized electric fields of the gold-nanoparticle film.

Electropolymerized Polythiophene Photoelectrodes with Density-Controlled Gold Nanoparticles

A polythiophene thin film was fabricated on gold nanoparticle (AuNP)-deposited indium-tin-oxide (ITO) electrodes with electropolymerization, whereas AuNPs were predeposited on the ITO surface. A photocurrent via photoexcited polythiophene increased with AuNPs which was attributed to the localized surface plasmon resonance. Investigation of the AuNP-density dependence on the relative enhancement of photocurrent revealed the maximum effect at 14% of AuNP-density, while 68% of AuNP-density exhibited smaller photocurrent than the polythiophene electrode without AuNPs. We have revealed that the effects of AuNPs saturate in the fairly low density region, and that the excess AuNPs even in the range of submonolayer resulted in the decrement of photocurrents.

Dichroism of Poly(vinylalcohol) Films Containing Gold Nanorods Induced by Polarized Pulsed-Laser Irradiation

Gold nanorods (NRs) dispersed in a poly(vinylalcohol) film were transformed into spherical particles by one shot of a pulsed-laser light (1064 and 532 nm, 6–7 ns). Irradiation by the linearly polarized laser light distinctly induced orientation-selective transformation of the NRs, which resulted in large dichroic properties of the film. The degree of the transformation depended on the wavelength as well as the polarization direction of the pulsed-laser light.

Solid-state solar cells consisting of polythiophene-porphyrin composite films

Sandwich-type solid-state solar cells using polythiophene-porphyrin composite films were fabricated. A spin-coated film of poly(3-dodecylthiophene) (P3DT) was fabricated on a gold electrode. Next, an electropolymerized polythiophene film was superimposed on the surface of the spin-coated P3DT film by electrochemical polymerization of bithiophene (BiTh) with repeated redox cycles in the 0–+2 V region. Then, tetrathienylporphyrin (TThP) was further assembled on the polythiophene-modified electrode by using the same electrochemical polymerization procedure (1 or 10 cycles), to obtain polythiophene-porphyrin-modified gold electrodes. Finally, an aluminum electrode was deposited on the polythiophene-porphyrin modified gold electrode by vacuum deposition, forming the sandwich-type solid-state solar cells. The morphological characterizations of the films were carried out by scanning electron microscopy. The thickness of the organic layer decreased from ~5 µm m to ~3 µm by performing TThP polymerization. The amount of porphyrin moiety in the composite film was larger for the modified electrode after 10 cycles of electrochemical TThP polymerization than for that after 1 cycle of TThP polymerization. The resultant photocurrent increased with scanning cycle of TThP polymerization in the 400–600 nm region. The combination of polythiophene and porphyrin in the electrochemically modified electrode is one of the useful systems for photocurrent generation.

Photoinduced intramolecular electron-transfer reactions in carbazole-fullerene and phenothiazine-fullerene linked compounds in benzene and benzonitrile as studied by fluorescence, transient absorption, time-resolved EPR, and magnetic field effects

Photoinduced intramolecular electron-transfer reactions in carbazole (Cz)-fullerene (C60) (Cz(8)C60) and phenothiazine (Ph)-C60 (Ph(n)C60 (n=8, 10, 12)) linked compounds have been investigated in benzene and benzonitrile by fluorescence, transient absorption, and time-resolved electron paramagnetic resonance measurements, and by magnetic field effects on the decay rate constants of the photogenerated biradicals. In benzonitrile, photoinduced intramolecular electron transfer from Cz to the singlet excited state of C60 (1C60*) occurred in Cz(8)C60, but not to the triplet excited state (3C60*), while the intramolecular electron-transfer to both1C60* and3C60* occurred in Ph(n)C60 (n=8, 10, 12). In benzene, on the other hand, no electron transfer to both1C60* and3C60* took place in all linked compounds. These results were interpreted in terms of the different Gibbs free energy changes in the two solvents.

Fabrication of Densely Packed Gold Nanoparticle Films and Their Fluorescence Enhancement Effect

Stable and densely packed two-dimensional films of gold nanoparticles (AuPs) were fabricated on a glass substrate, in which the gold nanoparticle film (AuPF) formed at a liquid/liquid interface was sandwiched between titanium oxide [Ti(O)] layers; the Ti(O) layer was prepared by a surface sol–gel process. The structure of AuPF on the substrate was measured and evaluated by absorption spectroscopy, quartz crystal microbalance (QCM) measurement, and scanning electron microscopy (SEM). Without the Ti(O) layer, the deposited gold nanoparticles moved to form aggregates on the substrate surface, as was verified from SEM measurements. A clear plasmon band due to AuPs was observed in the deposited AuPF both on the bare and Ti(O)-modified substrates. Tetratolylporphyrin (TTP) was cast on the surface of AuPFs. The excitation efficiencies of TTP on the as-described modified substrates were compared. The use of the Ti(O) layer was quite effective both for preserving the morphology of AuPF as well as for reducing the quenching effect of the photoexcited TPP by Au.

Pulsed-Laser Induced Fragmentation and Dissociation of DNA Immobilized on Gold Nanoparticles

ABSTRACT Plasmid DNA was immobilized on positively-charged gold nanoparticles (GNPs). Pulsed-laser irradiation induced fragmentation and dissociation of DNA from the GNP-DNA complexes. Dissociation of DNA without degradation was achieved when 80- mJ/pulse of laser light irradiated the GNP-DNA complexes.