Kinichi Morita

Mechanism of surface plasmon resonance sensing by indirect competitive inhibition immunoassay using Au nanoparticle labeled antibody

We investigated the use of a surface plasmon resonance (SPR) biosensor using an antibody (Ab) labeled with Au-nanoparticle (Ab-AuNP conjugate). As clenbuterol is a small molecule, an indirect competitive inhibition immunoassay was used. The SPR immunoassay using Ab-AuNP conjugate had an extremely low limit of the detection (LOD) with a magnitude of 0.05 ppt (0.05pgmL-1), which was 40 times lower than that of unlabeled Ab. To identify the key factor in determining the LOD of the indirect competitive inhibition immunoassay, affinity constants of the surface immunoreaction (K1) and of the premixed solution (αK2) were evaluated. We found that the dielectric constant change due to AuNP labeling of Ab did not affect on the affinity constants, because all the amplification magnitude terms canceled out in the equations. Thus, the K1 and αK2 values were determined to 3.0×1011M-1 and 2.9×1012M-1, respectively, which were three and four orders of magnitude higher, respectively, than those of unlabeled Ab. The simulation plot of LOD with respect to K1 and αK2 showed that a K1 one order of magnitude lower than αK2 produced a ppt level LOD. Because the affinity constants are determined by the molar concentrations of reactant and product, the molar mass of the Ab or Ab-AuNP conjugate in the sample solution containing 1ppm (1μgmL-1) highly affects the constants. Consequently, molar mass adjustment can be used to adjust the LOD in an indirect competitive inhibition immunoassay as needed for a practical application.

Carbon–polydimethylsiloxane-based integratable optical technology for spectroscopic analysis

A polydimethylsiloxane (PDMS)-based optical system has been demonstrated. To suppress intense background radiation due to multiple internal scatting in a transparent material, a composite structure of a carbon-PDMS compound and PDMS was proposed. The index matching of the real part of the refractive index can suppress internal scattering, and an absorption of 99-99.7% was attained by using carbon micro particles and carbon nano tubes. The black-PDMS light channel functions as a light filter for straight pass, and an optical density of 5 was obtained by bending the filter.

Gallium and polydimethylsiloxane molding for self-organized spherical lens surface fabrication

We present a new fabrication method for optical surfaces using liquid metal molding. Common optical surfaces are fabricated by the polishing of glasses or plastics. By contrast, the fabrication method we propose involves the transfer of a spherical surface of liquid molded metal with silicone rubber. The concept presented in this paper is of a new molding method in which a mold is placed inside. The curvature can be controlled from ∼0.37  mm−1 to −0.37  mm−1 by wetting the liquid metal. An application of this method is to produce on-demand optical elements (e.g., lenses and mirrors).

Highly sensitive detection of clenbuterol in urine sample by using surface plasmon resonance immunosensor

This study proposed the filtration method for removal of inhibitors from real urine samples for immunoassay without centrifuge. Although the inhibitors could not be removed by the physical filtration, the carboxyl group terminated silica effectively removed the inhibitors. In a low pH, antibody formed aggregation due to the protonation. We propose to adjust pH of the sample solution by adding a phosphate buffer solution (pH 7.5). As a result of pretreatment, the SPR immunosensing achieved the SPR signal of 45 mdeg and a low limit of detection with 100 ppq (100 fg mL-1).

Absorbance-meter constructed by PDMS

Novel scheme of polydimethylsiloxane-based optical system was proposed, and its measurement system combined with tablet type terminal has been demonstrated. Effective stray light reduction was observed in this scheme, and its mechanism have been studied. Scattering properties at the border between PDMS and carbon-doped PDMS was investigated, and discussed.