Hiromi Takiguchi

Liquid/Liquid Optical Waveguides Using Sheath Flow as a New Tool for Liquid/Liquid Interfacial Measurements

A liquid/liquid optical waveguide was constructed using a sheath flow. Since the refractive index of an organic solvent is generally higher than that of water (nD = 1.33), light introduced into the inner organic flow should proceed with total multi-reflection within the inner flow, so that the inner part of the sheath flow acts as the core of an optical waveguide. This sheath flow liquid/liquid optical waveguide was stable and showed no substantial background scattering. Moreover, it is applicable to both miscible and immiscible liquid/liquid interfaces. Thus, it may become a new tool for studying liquid/liquid interfaces as well as for sensitive optical measurements.

Surface Plasmon Resonance and Surface Plasmon Field-Enhanced Fluorescence Spectroscopy for Sensitive Detection of Tumor Markers

Surface plasmon resonance (SPR), which provides real-time, in situ analysis of dynamic surface events, is a valuable tool for studying interactions between biomolecules. In the clinical diagnosis of tumor markers in human blood, SPR is applied to detect the formation of a sandwich-type immune complex composed of a primary antibody immobilized on a sensor surface, the tumor marker, and a secondary antibody. However, the SPR signal is quite low due to the minute amounts (ng-pg/mL) of most tumor markers in blood. We have shown that the SPR signal can be amplified by applying an antibody against the secondary antibody or streptavidin-conjugated nanobeads that specifically accumulate on the secondary antibody. Another method employed for highly sensitive detection is the surface plasmon field-enhanced fluorescence spectroscopy-based immunoassay, which utilizes the enhanced electric field intensity at a metal/water interface to excite a fluorophore. Fluorescence intensity attributed to binding of a fluorophore-labeled secondary antibody is increased due to the enhanced field in the SPR condition and can be monitored in real time.

Effect of dielectric spacer thickness on signal intensity of surface plasmon field-enhanced fluorescence spectroscopy.

Surface plasmon field-enhanced fluorescence spectroscopy (SPFS) combines enhanced field platform and fluorescence detection. Its advantages are the strong intensity of the electromagnetic field and the high signal/noise (S/N) ratio due to the localized evanescent field at the water/metal interface. However, the energy transfer from the fluorophore to the metal surface diminishes the fluorescence intensity, and this reduces the sensitivity. In this study, we tested whether polystyrene (PSt) could act as a dielectric layer to suppress the energy transfer from the fluorophore to the metal surface. We hypothesized that this would improve the sensitivity of SPFS-based immunoassays. We used α-fetoprotein (AFP) as a model tumor biomarker in the sandwich-type immunoassay. We determined the relationship between fluorescent signal intensity and PSt layer thickness and compared this to theoretical predictions. We found that the fluorescence signal increased by optimally controlling the thickness of the PSt layer. Our results indicated that the SPFS-based immunoassay is a promising clinical diagnostic tool for quantitatively determining the concentrations of low-level biomarkers in blood samples.

Surface plasmon field-enhanced fluorescence spectroscopy apparatus with a convergent optical system for point-of-care testing.

Surface plasmon field-enhanced fluorescence spectroscopy (SPFS) is a promising methodology for point-of-care (POC) testing. The SPFS devices that have been reported are equipped with an angle rotating stage to adjust the surface plasmon resonance (SPR) angle. In a clinical setting, however, the SPR angle determination is a tedious and time-consuming process. In this study, we employed an SPFS instrument with a convergent optical system that allows the omission of this procedure. We demonstrated that this instrumentation allowed the sensitive determination of low concentrations of α-fetoprotein in serum and reduced the variation effect caused by the protein concentrations in samples. The SPFS with a convergent optical system is suitable for POC testing.

Development of Liquid/Liquid Optical Waveguide Using a Two Phase Sheath Flow and Its Application to Fluorescent Determination of Rhodamine B

Proposed was the use of a sheath flow as a liquid/liquid optical waveguide, in which the inner flow works as core and the outer flow as clad. Firstly, the conditions to obtain a stable liquid/liquid optical waveguide were investigated: the stable waveguide was constructed with using toluene, diethyl eter and THF as an inner phase, which are miscible or immiscible with water. Furthermore, fluorescence spectra of rhodamine B excited by evanescent wave at the liquid/liquid interface of the waveguide were obtained and the effect of solvents on the fluorescent spectra was discussed.

Development of Tetrahydrofuran/Water Optical Waveguide and Its Application to the Observation of Extraction Behavior of 1-Anilino-8-naphtalene Sulfonate at the Tetrahydrofuran/Water Interface

A stable two-phase sheath flow using tetrahydrofuran (THF) for an inner flow and water for an outer flow was formed in a glass capillary, and worked as a stable liquid-core/liquid-cladding optical waveguide (THF/water LLW). Although THF and water were miscible with any ratio, the length of the stable THF/water LLW at 0.9 - 2.1 cm s-1 reached at least 150 mm. The THF/water LLW was applied to the observation of extraction behavior of solvatochromic fluorescence dye, 1-anilino-8-naphtalene sulfonate (ANS), through the THF/water interface. ANS was added to the water phase (clad solution) and its fluorescence, which was excited with the guided light (355 nm) through the LLW, was observed by changing the position of the detector. While the ANS stayed in the region of 70% THF to the end of the LLW without the addition of cationic surfactant, hexadecyltrimethylammonium ion (CTA+) at pH 3 and 11, the ion-pair of ANS and CTA+ was extracted into the higher concentration region of THF with the addition of CTA+ at pH 11.