| Summary: | 碩士 === 國立成功大學 === 光電科學與工程研究所 === 95 === Surface plasmon resonance (SPR) biosensors have the advantages of high sensitivity, label free, and real-time analysis. Their high sensitivity is based on the enhancement of the local electric field while SPR occurs and the change of the resonance condition changed easily by environmental altering. By analyzing the resonance signal, we can quantitatively determine the environmental altering, such as the change of film thickness, refractive index of buffer solution, and extrinsic biomolecular adsorption. This study develops a coupled waveguide-surface plasmon resonance (CWSPR) biosensor with a subwavelength grating structure. It can not only improve the measurement resolution but also remain the detection sensitivity. Its optical setup, wavelength interrogation with normally incident white light source, provides parallel detection ability. However, the detection signal will be disturbed when a normal incident light via buffer solution. If we exchange the incident direction from the buffer solution side into the glass substrate, we observe that the electric field enhancement at the metal-buffer solution interface is very weak by simulation. Therefore, how to excite the SPR on the metal-buffer solution interface by changing the resonance condition through modulating the grating structure is also the subject of this study.
In this study, we first employ rigorous coupled wave analysis (RCWA) to analyze the reflective and the transmitted efficiencies of the subwavelength grating. Then, we use a finite-difference time-domain (FDTD) method to analyze the distribution of the electro-magnetic field in every layer of the structure. We can optimally design CWSPR biosensors with subwavelength grating structure by utilizing these two analysis methods and fabricate them by using e-beam lithography and semiconductor manufacturing technology. The experimental results to test the sensitivity of different kinds of buffer solutions demonstrate that the CWSPR biosensor has the ability to detect the environmental changes at the interface between metal and buffer solution. Finally, by modulating the grating structure, the SPR can be excited at the metal-buffer solution interface even the light is incident from the glass substrate.
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