An evanescent-field-coupled waveguide-mode (EFC-WM) sensor utilizes monolithic SiO₂/Si/SiO₂ sensing plates having a multilayered structure and is used to evaluate a blocking agent comprising poly(ethylene glycol)-based block copolymers. Factor IX (FIX) protein was detected using its aptamer, viz. FIX was immobilized on a glutaraldehyde-modified silica surface, and then treated with a biotinylated aptamer. The quantitative analysis of FIX was carried out using streptavidin-conjugated gold nanoparticles (SA-GNPs). The blocking polymer, poly(ethylene glycol)-b-poly(acrylic acid) (PEG-b-PAAc), was found to mask unreacted amine and glutaraldehyde (Glu) moieties on the SiO₂ surface, and it completely prevented the non-specific binding of SA-GNPs. By exploiting the strong blocking effect of PEG-b-PAAc, we achieved high ligand–analyte interaction sensitivity (sensitive down to 100 pM). To improve the sensitivity further, we also used pentaethylenehexamine-terminated PEG (N6-PEG) on GNPs. The improvement in sensitivity was found to be 1000-fold (to 100 fM), which was substantiated by the observation of higher numbers of GNPs on the sensing surface in the results of the scanning electron microscopic examination. Based on the competition assay of free biotin premixed with SA-GNPs, it was concluded that some active biotin-binding sites on the streptavidin were blocked by N6-PEG, which improved the binding ability to the biotinylated sensing surface. An optimum number of binding sites on the SA-GNPs might improve their binding affinity. The strategy shown with dual polymers, viz. blocking of the sensor chip surface and coating of SA-GNPs, is recommended for developing sensors with higher sensitivity and reliability. Selective binding of the aptamer to a very small amount of FIX in the mixed sample containing FXIa and FVIIa, or albumin, makes this the optimal strategy for detecting a FIX deficiency in human blood samples.

Paramagnetic centers and absorption bands induced by ultraviolet photons in Ge-doped ${\mathrm{SiO}}_2$ glass are investigated. Four kinds of samples with different Ge contents were exposed to ultraviolet photons from a KrF excimer laser (5.0 eV), a XeCl excimer lamp (4.0 eV), and a KrCl excimer lamp (5.6 eV). Irradiation with the KrF excimer laser induces two paramagnetic centers, named Ge(1) and Ge(2), in proportion with a decrease in the absorption at 5.1 eV and with an increase in absorption at 4.5 and 5.8 eV. The total density of the induced paramagnetic centers is linearly proportional to each induced change of the three absorption components and their proportionality constants are independent of the Ge content of the samples. The 4.0-eV photons from the XeCl excimer lamp induce only a Ge $E^{\prime }$ center, while the 5.6-eV photons from the KrCl excimer lamp induce a Ge(1) besides a Ge $E^{\prime }$ center. From these results, Ge(1) and Ge(2) are, respectively, assigned to the Ge electron center (GEC) and the positively charged Ge oxygen-deficient center $(\mathrm{GODC}{)}^{+},$ which donated an electron to the GEC. The oscillator strength of the GODC for the absorption at 5.1 eV was found to be 0.1. From this, it is considered that the GODC that acts as the electron donor is the Ge lone pair center (GLPC). Thermally stimulated luminescence (TSL) is also examined in Ge-doped ${\mathrm{SiO}}_2$ glass that was exposed to photons from the KrF excimer laser. The TSL spectrum is very similar to the photoluminescence spectrum that is known to be due to the GLPC’s. It was found that the absorption, which was induced by the KrF excimer laser photons, decreases during the TSL measurement and that this decrement of the absorption is proportional to the TSL intensity. As mentioned above, the electrons that are to be trapped to generate the GEC’s are released from the GLPC’s during the photon irradiation. Then, in its reverse reaction, these electrons are thermally detrapped from the GEC’s to regenerate the GLPC’s, and the TSL is caused by an electronic de-excitation in such formed GLPC’s. To conclude, the TSL phenomenon further validates the assumption that the GLPC is the electron donor to generate the GEC’s.

A highly sensitive biosensor to detect norovirus in environment is desired to prevent the spread of infection. In this study, we investigated a design of surface plasmon resonance (SPR)-assisted fluoroimmunosensor to increase its sensitivity and performed detection of norovirus virus-like particles (VLPs). A quantum dot fluorescent dye was employed because of its large Stokes shift. The sensor design was optimized for the CdSe-ZnS-based quantum dots. The optimal design was applied to a simple SPR-assisted fluoroimmunosensor that uses a sensor chip equipped with a V-shaped trench. Excitation efficiency of the quantum dots, degree of electric field enhancement by SPR, and intensity of autofluorescence of a substrate of the sensor chip were theoretically and experimentally evaluated to maximize the signal-to-noise ratio. As the result, an excitation wavelength of 390nm was selected to excite SPR on an Al film of the sensor chip. The sandwich assay of norovirus VLPs was performed using the designed sensor. Minimum detectable concentration of 0.01ng/mL, which corresponds to 100 virus-like particles included in the detection region of the V-trench, was demonstrated.