Hironobu Hori

Optical microscopic observation of fluorescence enhanced by grating-coupled surface plasmon resonance

On the substrate carrying a sub-wavelength grating covered with a thin metal layer, a fluorescent dye-labeled cell was observed by fluorescence microscope. The fluorescence intensity was more than 20 times greater than that on an optically flat glass substrate. Such a great fluorescence enhancement from labeled cells bound to the grating substrate was due to the excitation by grating coupled surface plasmon resonance. The application of a grating substrate to two-dimensional detection and fluorescence microscopy appears to offer a promising method of taking highly sensitive fluorescence images.

Surface profile dependence of the photon coupling efficiency and enhanced fluorescence in the grating-coupled surface plasmon resonance

The fluorescence excited by the enhanced electric field of grating-coupled surface plasmon resonance was detected on biochips. The enhancement of the electric field on a metallic grating surface was calculated using the finite difference time domain method for rectangular, trapezoidal, and sinusoidal models to clarify the grating-surface profile dependence of the enhanced fluorescence. The computational results showed that the enhancement in the trapezoidal model was stronger than that in the other models, and that the groove depth dependence of the enhancement in the trapezoidal model agreed well with the experimental data. The grating surface profile, including the groove depth, was found to be an important parameter of the grating structure for it to couple effectively with light.

Duty ratio-dependent fluorescence enhancement through surface plasmon resonance in Ag-coated gratings

One-dimensional gratings with different duty ratios were designed and implemented for enhanced fluorescence detection and imaging. Verified by finite difference time domain simulations, our results showed that the enhancement strongly depended on the duty ratio of the land width to pitch of the grating structure. The maximum enhancement factor was achieved when the duty ratio was equal to 0.50 in our trapezoidal gratings with pitch=400 nm and depth=20 nm. Such a facile grating mold will exert a considerable influence on microarray biosensors and fluorescence microscopy.

Alignment Control of Columnar Liquid Crystals for Uniformly Homeotropic Domain with Circularly Polarized Infrared Irradiation

In this study, the alignment change with circularly polarized infrared irradiation for columnar mesophase was investigated for a liquid crystalline triphenylene derivative in order to get uniform domain with homeotropic alignment of columnar liquid crystal. It was found that circularly polarized infrared irradiation provides alignment change to form new domain with uniformly homeotropic (“face-on”) alignment and this phenomena is by way of the excitation of the selected vibrational mode of a chemical bond. The results strongly imply that the infrared irradiation is a possible technique for device fabrication by use of columnar liquid crystalline semiconductors.