表面電漿子共振(surface plasmon resonance，SPR)生物感測技術具有高靈敏度、無須標定待測物及即時偵測等優點，而其高靈敏度乃來自於共振條件發生時，所產生的局域電場強化現象，以及易受到微小外來物破壞其共振條件進而藉由量測其訊號改變來定量分析外來物。本研究所發展的以次波長光柵建構之耦合波導表面電漿子共振(coupled waveguide-surface plasmon resonance，CWSPR)生物感測器不僅能改善量測精度亦能維持感測靈敏度，而以多波長光源正射的光學架構則能實現大量平行篩檢之能力，然而卻會因水系統之擾動干擾量測訊號。但是若以相同架構改由玻璃基板處入射，經由模擬結果發現會有金屬膜層與緩衝溶液界面之SPR效應的電場強化現象十分微弱及靈敏度降低的問題，因此如何藉由調整光柵參數改變SPR條件使光源由玻璃基板入射亦能激發金屬與緩衝溶液界面之SPR現象，避免原來架構下會產生之水系統擾動問題，也是本研究的主題。
本論文先以嚴格耦合波分析法(rigorous coupled wave analysis，RCWA)來設計分析入射光經次波長光柵繞射的反射及穿透效率，再以有限時域差分法(finite-difference time-domain method，FDTD method)加以模擬計算得到於各膜層介面之電磁場強化分佈情形，並以此二分析方法得到最佳的光柵與波導結構參數。利用半導體微影製程技術來製作此次波長建構之CWSPR生物感測器，並經過通以不同的溶液動態量測實驗，驗證其具有偵測環境變化之能力。最後，經由FDTD模擬分析確認改變光柵參數能使光源由玻璃基板入射亦能激發金屬與緩衝溶液界面之SPR，產生局域電磁場強化。

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.

1.　S.-J. Chen, F.-C. Chien, G.-Y. Lin, and K.-C. Lee, “Enhancement of the resolution of surface plasmon resonance biosensors by control of the size and distribution of nanoparticles,” Opt. Lett. 29, 1390 (2004).
2.　J.-N. Yih, Y.-M. Chu, Y.-C. Mao, W.-H. Wang, F.-C. Chien, K.-L. Lee, P.-K. Wei, and S.-J. Chen, “Optical waveguide biosensors constructed with sub-wavelength gratings,” Appl. Opt. 45, 1938 (2006).
3.　F.-C. Chien, C.-Y. Lin, J.-N. Yih, K.-L. Lee, C.-W. Chang, P.-K. Wei, C.-C. Sun, and S.-J. Chen, “Coupled waveguide- surface plasmon resonance biosensor with subwavelength grating,” Biosens. Bioelectron. 22, 2737 (2007).
4.　H. Raether, Surface Plasmons on Smooth and Rough Surfaces and on Gratings, Berlin: Springer-Verlag, (1988).
5.　易政男，藉由奈米電漿子偵測信號強化之表面電漿共振與表面強化拉曼散射生物感測器，中央大學光電所，九十四學年博士論文。
6.　B. Liedberg, C. Nylander, and I. Lundstrom, “Surface plasmon resonance for gas detection and biosensing,” Sens. Actuat. 4, 299 (1983).
7.　W. P. Chen and J. M. Chen, “Use of surface plasma waves for determination of the thickness and optical constants of thin metallic films,” J. Opt. Soc. Am. 71, 189 (1981).
8.　M. Specht, J. D. Pedarnig, W. M. Heckl, and T. W. Hänsch, “Scanning plasmon near-field microscope,” Phys. Rev. Lett. 68, 476 (1992).
9.　W. Srituravanich, N. Fang, S. Durant, M. Ambati, C. Sun, and X. Zhang, “Sub-100 nm lithography using ultrashort wavelength of surface plasmons,” J. Vacuum Science & Tech. B 22, 3475 (2004).
10.　J. Tominoga, J. Kim, H. Fuji, D. Büchel, T. Kikukawa, L. Men, H. Fukuda, A. Sato, T. Nakano, A. Tachibana, Y. Yamakawa, M. Kumagai, T. Fukaya, and N. Atoda, “Super-Resolution Near-Field Structure and Signal Enhancement by Surface Plasmons,” Jpn. J. Appl. Phys. 40, 1831 (2001).
11.　S. Maier, P. Kik, H. Atwater, S. Meltzer, E. Harel, B. Koel, and A. Requicha, “Local detection of electromagnetic energy transport below the diffraction limit in metal nanoparticle plasmon waveguides,” Nat. Mater. 2, 229, (2003).
12.　J. Homola, S. Yee, and G. Gauglitz, “Surface plasmon resonance sensors: review,” Sens. Actuat. B 54, 3 (1999).
13.　K. Cottier, M. Wiki, G. Voirin, H. Gao, and R. E. Kunz, “Label-free highly sensitive detection of (small) molecules by wavelength interrogation of integrated optical chips,” Sens. Actuat. B 91, 241 (2003).
14.　B. Cunningham, P. Li, B. Lin, and J. Pepper, “Colorimetric resonant reflection as a direct biochemical assay technique,” Sens. Actuat. B 81, 316 (2002).
15.　M. Levene, J. Korlach, S. Turner, M. Foquet, H. Craighead, and W. Webb, “Zero-mode waveguides for single-molecule analysis at high concentrations,” Science 299, 682 (2003).
16.　J. Dostálek, J. Homola, and M. Miler, “Rich information format surface plasmon resonance biosensor based on array of diffraction gratings,” Sens. Actuat. B 107, 154 (2005).
17.　K. Welford, “The method of attenuated total reflection,” IOP Short Meeting Series 9, 25 (1987).
18.　M. Moharam and T. Gaylord, “Rigorous coupled-wave analysis of planar-grating diffraction,” J. Opt. Soc. Am. 71, 811 (1981).
19.　J. Chinn, I. Adesida, E. Wolf, and R. Tiberio, “Reactive ion etching for submicron structures,” J. Vac. Technol. 19, 1418 (1981).
20.　J. Coburn, “Plasma-Assisted Etching,” Plasma Chem. Plasma Process. 2, 1 (1982).
21.　I. Hooper and J. Sambles, “Surface plasmon polaritons on thin-slab metal gratings,” Physical Review B 67, 235404 (2003).
22.　U. Schröter and D. Heitmann, “Grating couplers for surface plasmons excited on thin metal films in the Kretschmann-Raether configurtion,” Physical Review B 60, 4992 (1999).