Kazuyoshi Kurihara

Asymmetric SPR sensor response curve-fitting equation for the accurate determination of SPR resonance angle

Abstract An asymmetric surface plasmon resonance sensor response curve (SPR curve) equation derived from the three-layer Fresnel equation regarding p-polarization was proposed that can be used as a more general and appropriate SPR curve equation than Kretschmann’s equation given by R(X)=(1−α)/{(X−β)2+γ2}, where R is the reflectance of the incident light, α, β and γ are real parameters, and X the incident angle. The proposed equation is expressed as R(X)=A[1−{B+C(X−D)}/{(X−D)2+E2}] with a minimum reflectance at a conventional resonance angle of X=D+(−B+ B 2 +C 2 E 2 )/C , where A, B, C, D and E are five real parameters that are very useful as fitting functions for a gold-based SPR curve in real-time measurement. In this equation, a modified resonance angle defined as parameter D is more appropriate than the conventional resonance angle as a variable that gives a linear response to changes in the refractive index of the sensing layer.

Imaging of electrochemical enzyme sensor on gold electrode using surface plasmon resonance.

Three types of imaging, namely layer structure, electrochemical reaction, and enzyme sensor response, were achieved by applying surface plasmon resonance (SPR) measurement to an electrochemical biosensor. We constructed glucose oxidase based mediator type sensors on a gold electrode by spotting the mediator that contained horseradish peroxidase and spin coating the glucose oxidase film. The layer structure of the sensor was imaged by means of angle scanning SPR measurement. The single sensor spot (about 1 mm in diameter) consisted of about 100 x 100 pixels and its spatial structure was imaged. The multilayer structure of the enzyme sensor had a complex reflectance-incident angle curve and this required us to choose a suitable incident angle for mapping the redox state. We chose an incident angle that provided the most significant reflection intensity difference by using data obtained from two angle scanning SPR measurements at different electrode potentials. At this incident angle, we controlled the electrochemical states of the spotted mediator in cyclic voltammetry and imaged the degree to which the charged site density changed. Finally, we mapped the enzymatic activity around the mediator spot by the enzymatic reoxidation of pre-reduced mediator in the presence of glucose.

Superfocusing modes of surface plasmon polaritons in a wedge-shaped geometry obtained by quasi-separation of variables

Analytic solutions to the superfocusing modes of surface plasmon polaritons in the wedge-shaped geometry are theoretically studied by solving the Helmholtz wave equation for the magnetic field using quasi-separation of variables in combination with perturbation methods. The solutions are described as a product of radial and extended angular functions and are obtained for a lossless metallic wedge and V-groove by determining the separation quantities that satisfy the boundary conditions. For the metallic wedge and V-groove, we show that the radial functions of the zeroth order are approximately described by the imaginary Bessel and modified Whittaker functions, respectively, and that the extended angular functions have odd and even symmetries, respectively, for reflection in the central plane of the wedge-shaped geometry. Importantly, we show that the wave numbers of superfocusing surface plasmon polaritons in the metallic wedge and V-groove are clearly different in their radial dependence.

Superfocusing modes of surface plasmon polaritons in conical geometry based on the quasi-separation of variables approach

Analytic solutions to the superfocusing modes of surface plasmon polaritons in a conical geometry are theoretically studied using an ingenious method called the quasi-separation of variables. This method can be used to look for fundamental solutions to the wave equation for a field that must satisfy boundary conditions at all points on the continuous surface of tapered geometries. The set of differential equations exclusively separated from the wave equation can be consistently solved in combination with perturbation methods. This paper presents the zeroth-order perturbation solution of conical superfocusing modes with azimuthal symmetry and graphically represents them in electric field-line patterns.

SPR sensor signal amplification based on dye-doped polymer particles

Abstract A novel amplification method was prepared based on dye-doped polymer particles for SPR signals originating from antigen–antibody (BSA–anti-BSA) interactions. Coloring the particles enhances the change of SPR signals based on the change of the imaginary part of the refractive index. The signal amplification effect in the reflectance mode was 31-fold stronger compared to the effect obtained with white latex particles and the combined amplification effect due to the presence of polymer particles and the colorant was over 100-fold compared to non-amplified SPR signals originating from BSA–anti-BSA interactions. The amplification method based on the dye-doped particles is widely applicable for the analysis of antibody–antigen interactions and DNA interactions at low concentrations.

Highly sensitive electro-optic sampling of terahertz waves using field enhancement in a tapered waveguide structure

We report on increasing the sensitivity of electro-optic sampling detection of terahertz pulses by using the effect of terahertz field enhancement in a tapered metallic waveguide. A thin Si prism, placed in the narrower section of the waveguide, is used to synchronize the enhanced terahertz field with the probe laser pulse propagating in a LiNbO3 crystal attached to the obliquely cut end of the waveguide. A 40-µm-thick MgO-doped layer on the surface of LiNbO3 is used for guiding the probe pulse. The developed structure demonstrates a 20-fold higher detection sensitivity than a no-waveguide, Si-prism-coupled LiNbO3 crystal.

Comparative study of Nd:YAG laser-induced breakdown spectroscopy and transversely excited atmospheric CO2 laser-induced gas plasma spectroscopy on chromated copper arsenate preservative-treated wood.

Taking advantage of the specific characteristics of a transversely excited atmospheric (TEA) CO(2) laser, a sophisticated technique for the analysis of chromated copper arsenate (CCA) in wood samples has been developed. In this study, a CCA-treated wood sample with a dimension of 20 mm × 20 mm and a thickness of 2 mm was attached in contact to a nickel plate (20 mm × 20 mm × 0.15 mm), which functions as a subtarget. When the TEA CO(2) laser was successively irradiated onto the wood surface, a hole with a diameter of approximately 2.5 mm was produced inside the sample and the laser beam was directly impinged onto the metal subtarget. Strong and stable gas plasma with a very large diameter of approximately 10 mm was induced once the laser beam had directly struck the metal subtarget. This gas plasma then interacted with the fine particles of the sample inside the hole and finally the particles were effectively dissociated and excited in the gas plasma region. By using this technique, high precision and sensitive analysis of CCA-treated wood sample was realized. A linear calibration curve of Cr was successfully made using the CCA-treated wood sample. The detection limits of Cr, Cu, and As were estimated to be approximately 1, 2, and 15 mg/kg, respectively. In the case of standard LIBS using the Nd:YAG laser, the analytical intensities fluctuate and the detection limit was much lower at approximately one-tenth that of TEA CO(2) laser.

Diffraction-grating-type phase converters for conversion of Hermite-Laguerre-Gaussian mode into Gaussian mode

Diffraction gratings that can be used to convert the Hermite-Laguerre-Gaussian (HLG) mode into the Gaussian mode were obtained; these modes are space modes of light beams. The HLG mode is intermediate between the Hermite-Gaussian and the Laguerre-Gaussian modes. Generally, gratings produced from interfering two beams as holograms contain information of not only the phase modulation factor but also the amplitude modulation factor. Thus, they cannot be expected to provide high conversion efficiency. To produce high-efficiency gratings, the interference equation is divided into two factors. The gratings produced by considering only the phase factors act as phase converters.

Imaging of flow pattern in micro flow channel using surface plasmon resonance

We describe the visualization of the mixing and control of flow patterns in micro fluidic devices using a surface plasmon resonance (SPR) imaging sensor. We employed Kretschmann-type prism coupling SPR optics and an expanded laser diode light source via a single mode optical fibre. The reflected light was focused on a CCD camera. Two types of micro fluidic device were fabricated using photolithography and polymer imprinting a 2 mm wide, 100 µm high channel flow cell for the mixing and a slab channel device for flow control. We were able to observe mixing in the flow channel in real time with SPR imaging as the local refractive index change. Because the sensitivity of this system was limited within wavelength long distance from the gold surface, we could image the flow condition very near the channel wall. We also succeed in delivering the flow to a part of 4 × 4-array sensing area in a slab flow channel. These results will assist the development of integrated biosensors.

Rapid Analyses of Tiny Amounts of Powder Samples Using Transversely Excited Atmospheric CO2 Laser-Induced Helium Gas Plasma with the Aid of High-Vacuum Silicon Grease as a Binder on a Metal Subtarget

Rapid quantitative analyses of powder samples available in tiny amounts have successfully been conducted by utilizing a transversely excited atmospheric (TEA) CO2 laser-induced He gas plasma. In this study, 4 mg of powder sample was homogeneously mixed with 4 mg of high-vacuum silicon grease and the silicon grease–mixed powder sample (SMP) was painted on a metal surface, which serves as a subtarget. The grease functions to strongly bind the powder and to suppress blow-off of the powder particles. When a TEA CO2 laser (750 mJ, 10.6 μm, 200 ns) was directly focused on the metal subtarget in He gas at 1 atmosphere, a hightemperature He gas plasma was induced, producing a profusion metastable He atoms. It is assumed that the powder particles together with the silicon grease were vaporized to be effectively atomized and excited through metastable He atoms. The result revealed that this technique can be widely employed in the rapid semi-quantitative analyses of powder samples present in minute amounts. A quantitative analysis of loam soil containing different concentrations of Cu was successfully demonstrated, resulting in a good linear calibration curve. The detection limits of Cr and Pb in loam soil were approximately 4 and 13 mg/kg, respectively. Also, we confirmed that this technique can be applied to check the quality of commercial products such as gold film (Au foil), mineral supplement tablets, and prestigious cosmetic powders.