Vol.8 No.2 2015
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Research paper : Detection of influenza viruses with the waveguide mode sensor (K. AWAZU et al.)−100−Synthesiology - English edition Vol.8 No.2 (2015) Since it was possible to measure using the waveguide modes by sweeping the wavelength, we designed an optical system as shown in Fig. 3. The excitation light reached the back of the measuring site as white light, and the reflected light passed through the collimator lens and optical fiber and reached the spectrometer. The four-point measurement was possible at the measuring site using four light sources. The two goniometers for sweeping while synchronizing became unnecessary in this optical system, and this enabled size reduction.Figure 4 is a detailed diagram of the measuring site of Fig. 3 during measurement. The detection plate that detected the surface reaction was a SiO2 glass substrate on which monocrystalline silicon (c-Si) film was formed, and it was obtained by thermally oxidizing silicon to obtain amorphous silica (a-SiO2). The mechanism was to sensitively detect the surface reaction by designing the thicknesses of c-Si film and a-SiO2 film so it would be possible to obtain the maximum reflectivity change against the refraction index change on this a-SiO2 layer surface. Figure 5 is the calculation of electric field intensity distribution near the detection plate surface at a wavelength of 512 nm, silica waveguide layer thickness of 284 nm, and monocrystalline silicon layer thickness of 220 nm. It can be seen that a strong electric field was formed on the waveguide layer surface, and this enabled highly sensitive detection. Therefore, it was possible to capture the refraction index change of the surface upon which the antibodies were fixed and then were made to react with the virus. Also, it was possible to amplify the signal with gold nanoparticles, as explained later.The process of size reduction is shown in Fig. 6. First, it was an angle-sweeping type where the optical system was set on a two stage plate at 1 m × 50 cm as shown in (a). Later, since it was possible to conduct measurement at waveguide mode by sweeping the wavelength as shown in Figs. 2 and 3, the optical system as shown in Fig. 3 was designed. The excitation light reached the back of the measuring site as white light, and the reflected light passed Fig. 3 Wavelength sweeping waveguide mode sensorWhite LED was used as the light source. The measuring plate was installed in the measurement site, and the reaction on the measuring plate was detected by reflected light. The reflected light could be led to the spectrometer by installing the optical fiber optical axis.Fig. 4 Optical arrangement of the waveguide mode sensorConfiguration of the SiO2 glass substrate on a prism and the detection plate was the same as Fig. 1. The outgoing light was dispersed by the spectrometer.Fig. 5 Electric field intensity distribution of waveguide modes at 220 nm c-Si layer, 284 nm SiO2 layer, and 512 nm excitation wavelengthSimilarly to Fig. 1, the yellow arrow is the direction of incoming and outgoing light. The film thickness and others were designed so the electric field intensity reached the maximum at the SiO2 layer surface. The scale bar on the side indicates electric field intensity.Fig. 2 Calculation results of the dependence of reflectivity change on angle and wavelengthThe quantity of reflectivity change is shown in color. The peak of reflectivity change was observed when the wavelength was fixed and the angle was swept, but it can also be seen that the peak of reflectivity change was observed when the angle was fixed and the wavelength was swept.Angle of incidence(°)Reflectivity difference-0.100.10.20.30.4-0.2-0.3-0.4-0.5800700600500400-0.500.5Wavelength (nm)657075Polarizing plateOptical fiberSpectrometerCollimeter lensPrismCollimeter lensLEDOptical fiberMeasuring site AntibodyVirusPolarizerSurface chemical reactionDiffraction grating, spectrometerLight source0 0.5 1 1.5 x (μm)7 6 5 4 3 2 1 0substratec-Sia-SiO2water012345671.510.50x(µm)

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