Anisotropic growth of Au-Ag heteronanostructures through plasmon-induced reduction.

Plasmonic heteronanostructures are promising building blocks for photofunctional materials and devices including photocatalysts, optical materials, and optoelectronic devices. In the present work, we fabricated Au-Ag bimetallic heteronanostructures based on site-selective and anisotropic Ag deposition and growth on Au nanocubes. Plasmonic Au nanocubes were adsorbed onto a glass plate, and the distal mode or proximal-distal mode of the nanocubes was selectively excited in the presence of Ag+ and citrate ions.

Active control of plasmon coupling simple electrochemical surface oxidation/reduction of Au nanoparticle agglomerates.

Reversible tuning of plasmon coupling of Au nanoparticle (AuNP) agglomerates containing dimers as the main component was achieved electrochemical surface oxidation/reduction of the AuNP surface. The system required no reactant except for water and was almost finished within a unit second, which leads to novel active plasmonic devices.

Site-selective introduction of MnO co-catalyst onto gold nanocubes via plasmon-induced charge separation and galvanic replacement for enhanced photocatalysis.

For energy harvesting with plasmonic photocatalysis, it is important to optimize geometrical arrangements of plasmonic nanomaterials, electron (or hole) acceptors, and co-catalysts so as to improve the charge separation efficiency and suppress charge recombination. Here, we employ a photocatalytic system with Au nanocubes on TiO and introduce MnO as an oxidation co-catalyst onto the nanocubes via site-selective oxidation based on plasmon-induced charge separation (PICS). However, it has been known that PbO is the only material that can be deposited onto Au nanomaterials through PICS with sufficient site-selectivity.

Spatial distribution of single guest molecules along thickness of thin films of poly(2-hydroxyethyl acrylate).

We have investigated three-dimensional distribution and diffusion behaviors of single guest dyes in 1-µm thick films of poly(2-hydroxyethyl acrylate) (PHEA) by using astigmatism imaging method. Perylene diimide derivative (BP-PDI) in the PHEA films localized along the Z-axis at ca. Z = 600-700 nm distant from the interface (Z = 0) between PHEA and glass substrate.

Visualization of nano-localized and delocalized oxidation sites for plasmon-induced charge separation.

Oxidation reaction sites for plasmon-induced charge separation at Au nanocubes on TiO2 were visualized on the basis of deposition and dissolution reactions. For Pb2+ oxidation, PbO2 was deposited selectively at resonance sites of the nanocube, while oxidation polymerization of pyrrole to polypyrrole and oxidative dissolution of Au took place over the entire nanocube surface. The localized and delocalized reaction sites are explained in terms of a relationship between oxidation potentials of the electron donors and potentials of the entire nanocube and localized holes.

Plasmonic hole ejection involved in plasmon-induced charge separation.

Since the finding of plasmon-induced charge separation (PICS) at the interface between a plasmonic metal nanoparticle and a semiconductor, which has been applied to photovoltaics including photodetectors, photocatalysis including water splitting, sensors and data storage in the visible/near-infrared ranges, injection of hot electrons (energetic electrons) into semiconductors has attracted attention almost exclusively. However, it has recently been found that behaviours of holes are also important. In this review, studies on the hot hole ejection from plasmonic nanoparticles are described comprehensively.

Accelerated site-selective photooxidation on Au nanoparticles via electrochemically-assisted plasmonic hole ejection.

In order to induce electrochemical reactions by localized surface plasmon resonance (LSPR), semiconductors have been employed as electron or hole acceptors for plasmon-induced charge separation (PICS) in most cases. Here we replaced a semiconductor with a potential-controlled transparent electrode, and achieved accelerated photooxidation reactions at selected local sites on plasmonic metal nanoparticles. We demonstrate site-selective PbO deposition at the tips and sides of Au nanorods and PbO deposition and Au dissolution at the top and bottom of Au nanocubes, through the selective excitation of different LSPR modes.

Plasmon-induced charge separation at the interface between ITO nanoparticles and TiO under near-infrared irradiation.

Plasmon-induced charge separation (PICS) by continuous electron injection from plasmonic compound nanoparticles to a semiconductor was achieved by using solid-state cells based on tin-doped indium oxide (ITO) nanoparticles with a short capping agent and a TiO2 film. The cells extended the PICS range to longer wavelengths and exhibited photoresponses to 1500-2200 nm near-infrared light.

Local trapping of energetic holes at gold nanoparticles on TiO.

Oxidation sites for plasmon-induced charge separation at gold nanocubes and nanorods on TiO2 were visualized by PbO2 deposition, and the sites were localized at plasmonic resonance sites. This indicates that energetic holes generated at those sites dominate the reactions, which can be applied to photo-nanofabrication beyond the diffraction limit.

Plasmonic behaviour and plasmon-induced charge separation of nanostructured MoO under near infrared irradiation.

Plasmon-induced charge separation (PICS) allows direct conversion of localized surface plasmon resonance (LSPR) to electron flows and photoelectrochemical reactions. However, PICS has only been achieved using plasmonic noble metal nanoparticles, not with compound nanoparticles. In order to achieve compound PICS, MoO nanostructures were prepared that exhibit LSPR in the near infrared region by using metal oxides or metal nanoparticles as templates.

Effects of particle size and annealing on plasmon-induced charge separation at self-assembled gold nanoparticle arrays.

Two-dimensional periodic Au nanoparticle arrays were constructed on TiO thin films by a micelle lithography method and seed-mediated photoelectrochemical growth. Their adjustable interparticle distance allows investigation of a particle size effect on plasmon-induced charge separation (PICS) efficiencies without interference from particle aggregation or plasmon coupling. External or internal PICS efficiencies were found to increase and decrease, respectively, with an increase in particle diameter from 25 to 38 nm.

Hydrogen evolution from water based on plasmon-induced charge separation at a TiO/Au/NiO/Pt system.

Metal-semiconductor plasmonic nanostructures are capable of converting light energy through plasmon-induced charge separation (PICS), providing fruitful new strategies to utilize solar energy in various fields, including photocatalysis. Here, we enhance the PICS efficiencies for hydrogen evolution from water at a Pt cathode coupled with a TiO/Au photoanode by coating the TiO/Au with a p-type NiO layer on which a Pt co-catalyst is deposited. PICS occurs at the Au-TiO interface under visible light.

Tunable plasmon resonance of molybdenum oxide nanoparticles synthesized in non-aqueous media.

Plasmonic compound nanoparticles (NPs) have attracted great interest because they are prepared at lower cost and show unique optical properties. However, full replacement of the plasmonic noble metal NPs with the compound NPs has been difficult because most of the compound NPs exhibit plasmon resonance in the infrared range owing to low free carrier density and mobility. In order to overcome this limitation, we developed a new synthetic method for plasmonic MoO and MoO NPs.

Potential-Scanning Localized Plasmon Sensing with Single and Coupled Gold Nanorods.

Single plasmonic nanoparticles can potentially serve as optical sensors for detecting local refractive index changes. However, simultaneous monitoring of the scattering spectra from multiple nanoparticles is not practical. Here we perform potential-scanning localized surface plasmon resonance (LSPR) sensing.

Plasmon-induced charge separation: chemistry and wide applications.

Recent development of nanoplasmonics has stimulated chemists to utilize plasmonic nanomaterials for efficient and distinctive photochemical applications, and physicists to boldly go inside the "wet" chemistry world. The discovery of plasmon-induced charge separation (PICS) has even accelerated these trends. On the other hand, some confusion is found in discussions about PICS.

Labeling and in vivo visualization of transplanted adipose tissue-derived stem cells with safe cadmium-free aqueous ZnS coating of ZnS-AgInS nanoparticles.

The facile synthesis of ZnS-AgInS (ZAIS) as cadmium-free QDs and their application, mainly in solar cells, has been reported by our groups. In the present study, we investigated the safety and the usefulness for labeling and in vivo imaging of a newly synthesized aqueous ZnS-coated ZAIS (ZnS-ZAIS) carboxylated nanoparticles (ZZC) to stem cells. ZZC shows the strong fluorescence in aqueous solutions such as PBS and cell culture medium, and a complex of ZZC and octa-arginine (R8) peptides (R8-ZZC) can achieve the highly efficient labeling of adipose tissue-derived stem cells (ASCs).

Controlling Shape Anisotropy of ZnS-AgInS Solid Solution Nanoparticles for Improving Photocatalytic Activity.

Independently controlling the shape anisotropy and chemical composition of multinary semiconductor particles is important for preparing highly efficient photocatalysts. In this study, we prepared ZnS-AgInS solid solution ((AgIn)ZnS, ZAIS) nanoparticles with well-controlled anisotropic shapes, rod and rice shapes, by reacting corresponding metal acetates with a mixture of sulfur compounds with different reactivities, elemental sulfur, and 1,3-dibutylthiourea, via a two-step heating-up process. The chemical composition predominantly determined the energy gap of ZAIS particles: the fraction of Zn in rod-shaped particles was tuned by the ratio of metal precursors used in the nanocrystal formation, while postpreparative Zn doping was necessary to increase the Zn fraction in the rice-shaped particles.

Oxidation Ability of Plasmon-Induced Charge Separation Evaluated on the Basis of Surface Hydroxylation of Gold Nanoparticles.

The oxidation ability of plasmonic photocatalysts, which has its origins in plasmon-induced charge separation and has not yet been studied quantitatively and systematically, is important for designing practical photocatalytic systems. Oxidation ability was investigated on the basis of surface hydroxylation of Au nanoparticles on TiO2 at various irradiation wavelengths and electrolyte pH values. The reaction proceeds only when the sum of the flat band potential of TiO2 and the irradiated photon energy is close to, or more positive than, the theoretical potential for the reaction.

Electrochemical redox-based tuning of near infrared localized plasmons of CuS nanoplates.

Fast and reversible control of the plasmonic properties of compound nanoparticles (i.e. CuS nanoplates) was achieved through electrochemical redox reactions.

Potential-Scanning Localized Surface Plasmon Resonance Sensor.

Localized surface plasmon resonance (LSPR) sensors based on plasmonic nanoparticles attract much attention recently. Here we propose a new class of LSPR sensor, that is, a potential-scanning LSPR sensor, in which electron density of the plasmonic nanoparticles is controlled by potential scanning. The sensor exhibits a resonance peak during the potential scan, which negatively shifts with increasing local refractive index.

Direct output of electrical signals from LSPR sensors on the basis of plasmon-induced charge separation.

Potentiometric and conductometric sensors based on localized surface plasmon resonance were developed. The sensors can be applied to coloured and turbid samples because light need not pass through the sample solution.

Wavelength- and efficiency-tunable plasmon-induced charge separation by the use of Au-Ag alloy nanoparticles.

TiO2 electrodes loaded with Au-Ag alloy nanoparticles, Ag content of which is about 0.25-0.90, exhibit stable anodic photocurrents due to plasmon-induced charge separation (PICS) in the presence of an electron donor.

Adipose Tissue-Derived Stem Cell Imaging Using Cadmium-Free Quantum Dots.

Quantum dots (QDs) have received much attention for biomolecule and cell imaging applications because of their superior optical properties such as high quantum efficiency, size-tunable emission, and resistance to photobleaching process. However, QDs that are commercially available contain cadmium (Cd), a highly toxic element. Thus, the development of Cd-free and less toxic QDs is strongly desired.

Controllable electronic energy structure of size-controlled Cu2ZnSnS4 nanoparticles prepared by a solution-based approach.

Cu2ZnSnS4 nanoparticles with sizes of 2-5 nm, synthesized in hot organic solutions, exhibited size-dependent photoelectrochemical properties due to the quantum size effect. The potentials of the valence band edge and conduction band edge of the nanoparticles, experimentally determined by photoelectrochemical measurements, were shifted more positively and more negatively, respectively, with a decrease in particle size.