Yoshito Tanaka

We performed two-dimensional mapping of optical trapping potentials experienced by a 100 nm dielectric particle above a plasmon-resonant gold nanoblock pair with a gap of several nanometers. Our results demonstrate that the potentials have nanoscale spatial structures that reflect the near-field landscape of the nanoblock pair. When an incident polarization parallel to the pair axis is rotated by 90°, a single potential well turns into multiple potential wells separated by a distance smaller tha

Optical force is a powerful tool to actuate micromachines. Conventional approaches often require focusing and steering an incident laser beam, resulting in a bottleneck for the integration of the optically actuated machines. Here, we propose a linear nanomotor based on a plasmonic particle that generates, even when illuminated with a plane wave, a lateral optical force due to its directional side scattering. This force direction is determined by the orientation of the nanoparticle rather than a

The biosynthesis of astaxanthin in the prawn was further studied using pure carotenoids and preparations obtained from natural sources. Zeaxanthin, obtained from the Chinese lantern, was fed to the prawn, Penaeus japonicus Bate. Astaxanthin was biosynthesized from zeaxanthin, thus indicating the existence of a second pathway to astaxanthin in the prawn. Canthaxanthin and astaxanthin from crab waste were respectively metabolized to and absorbed as body astaxanthin in the prawn. Pigmented preparat

The role of the NAD(P)H-dehydrogenase complex in adaptation to salt stress was examined in an ndhB-inactivated mutant of the cyanobacterium Synechocystis sp. PCC 6803. Wild-type cells and ndAfl-inactivated mutant cells grew at similar rates under conditions of low salinity (<0.6M NaCl) and high CO 2 (3%). However, when the concentration of NaCl in the culture medium was higher than 0.6 M, the mutant cells grew much more slowly than the wild-type cells. Upon addition of high concentrations of NaC

Achieving high directionality of scattered light in combination with high flexibility of the direction using plasmonic nanoparticles is desirable for future optical nanocircuits and on-chip optical links. The plasmonic characteristics of nanoparticles strongly depend on their geometry. Here, we studied directional light scattering by a single-element triangular plasmonic nanoparticle. Our experimental and simulation results demonstrated that the triangular nanoparticle spatially sorted the incom

Arbitrary spatial distributions of the electric field of light are formed through the interference of individual wavenumber mode fields with appropriate amplitudes and phases, while the maximum wavenumber in the far field is limited by the wavelength of light. In contrast, localized surface plasmons (LSPs) possess the ability to confine photons strongly into nanometer-scale areas, exceeding the diffraction limit. In particular, gap-mode LSPs produce single-nanometer-sized, highly intense localiz

We report laser induced self-assembly of silver nanoparticles via plasmonic interactions. By focusing a near-infrared laser in silver nanoparticle suspension, nanoparticle assembly is formed as a result of optical trapping. The shape of Rayleigh scattering spectra of the nanoassembly strongly depends on the polarization of the laser beam. Particularly, a linearly polarized laser induces the formation of arrayed structure along the laser polarization, that shows a sharp plasmon resonance band and

We have investigated a pseudoisocyanine dye aqueous solution including nanometer-sized J-aggregates by combining optical trapping and two-photon fluorescence spectroscopy. By focusing an intense near-infrared laser into an 8 x 10(-3) M solution, the intense fluorescence from J-aggregates for a few to tens of seconds is observed intermittently, indicating that individual J-aggregates are trapped in and diffuse out from a focal spot. The peak position and full width at half-maximum of the J-band a

We have investigated the plasmonic trapping of dielectric nanoparticles by using engineered gold nanoblock pairs with ~5-nm gaps. Pairs with surface-plasmon resonance peaks at the incident wavelength allow the trapping of 350-nm-diameter nanoparticles with 200 W/cm2 laser intensities, and their plasmon resonance properties and trapping performance are drastically modified by varying the nanoblock size of ~20%. In addition, plasmon resonance properties of nanoblock pairs strongly depend on the di

We have investigated surface enhanced Raman scattering (SERS) stemming from pseudoisocyanine (PIC) molecules adsorbed on Ag nanoparticles by using optical trapping techniques in aqueous solution. By focusing a near-infrared (NIR) laser beam with linear polarization in addition to a visible excitation laser beam, the PIC concentration necessary to detect SERS is dramatically reduced to 10−14 M, whereas no effect is confirmed with circular polarization. This finding suggests that optical trapping