Vol.2 No.2 2009

69/98

Research paper : Development of high-sensitivity molecular adsorption detection sensors (M. Fujimaki et al.)−149−Synthesiology - English edition Vol.2 No.2 (2009) it was assumed that a layer (light pink layers in Fig. 14) with a thickness of 5 nm and a refractive index of 1.45 was formed on the detection surface. Figures 14(d), 14(e), and 14(f) show the calculation results of the reflectance property before and after the molecule adsorption shown in Figs. 14(a), 14(b), and 14(c), respectively. In these sensors, the sensitivity is higher if the full-width at half maximum (W) of the dip is small and the shift of the peak position (S) is large. Namely, the sensitivity is higher if S/W values is higher. Table 2 shows the values of change in reflectance (R), S, W, and S/W caused by the molecule adsorption in the experiment and in the simulation. In case of the EFC-WM sensor without nanopores, almost all the values obtained in the experiment agree well with the values obtained in the simulation. In case of the EFC-WM sensor with nanopores, the S values were greater in the experiment value. To obtain the shift of S = 1.91 obtained in the experiment for calculation, the diameter and the number of the nanopores had to be set at 65 nm and 6 × 109 pores/cm2, respectively. This means that the diameter and the number of the nanopores formed in the experiment were slightly larger than those in the fabrication setting. As shown in Table 2, the value of S/W obtained in the experiment was 2.98 with nanopores, and 0.514 without nanopores. These values were both larger than the theoretical S/W value of the SPR sensor, and it was about 4 times greater without nanopores and about 25 times greater with nanopores.Monolithic sensing plate is excellent in stability. The monolithic plate is physically stable because the substrate, the reflective film, and the waveguide layer are atomically bonded to each other. Also, since it is composed only of Si and SiO2, it is chemically stable.4 BreakthroughTo apply this sensor to the actual detection of substance originating from various diseases, we conducted a hospital survey to see which substances should be targeted. In this survey, we realized that many sensors used at hospitals for similar purposes detect disease substance using color density. The monolithic sensing plate is sensitive to changes in refractive index as mentioned above, and it is even more sensitive to changes in optical absorption, or density of “color.” Therefore, we redesigned the sensor so it can detect changes in “color” more sensitively. The dip seen in the reflectance property of the EFC-WM sensor changes in the angle direction or along the horizontal axis direction against the change in refractive index, while for the change in optical absorption, it changes in reflectance intensity or vertical axis direction. Therefore, we changed the structure of the Table 2 Comparison of sensitivity of SPR and EFC-WM sensors. Sim. is calculated values, and Ex. is experimental values.SPR sensor Sim.EFC-WM sensor without nanopores Sim.EFC-WM sensor without nanopores Ex.EFC-WM sensor with nanopores Sim.EFC-WM sensor with nanopores Ex.0.150.380.400.600.63ΔRS1.00゜1.91゜0.17゜0.19゜0.72゜W8.4゜0.64゜0.34゜0.37゜0.34゜S/W0.120.510.492.982.12Fig.14 Conceptual diagram of molecule adsorption in the SPR sensor (a), the EFC-WM sensor without nanopores (b), and the EFC-WM sensor with nanopores (c). (d), (e), and (f) show the calculation results of reflectance property before and after the molecule adsorption in (a), (b), and (c), respectively.(f)(e) (d) (c)(b)(a) SiWSReflectanceWaveguideSiProteinAuΔRWSΔRWSΔR5060708000.20.40.60.8100.20.40.60.8100.20.40.60.81697071726566676968Angle of incidence(degrees)Angle of incidence(degrees)Angle of incidence(degrees)

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