改善表面電漿波側向傳播之對稱介電質結構設計與應用

Abstract

表面電漿共振(Surface plasmon resonance, SPR)現象應用於光學檢測已有數十年，在一般所使用的角度調變量測方法中，所使用之金膜厚度為50nm，在可見光範圍內，SPR曲線圖半高寬約為4°~6°，半高寬愈大代表檢測愈不靈敏，因此仍有將半高寬縮小、敏感度提高的改善空間。傳統的研究均以表面電漿波在垂直介面方向上的感測為主，而其垂直方向的穿透深度大約在100nm~200nm的範圍，能變動的範圍不大，對其感測的範圍有了限制，只有在這100nm~200nm深度的分子才能被感測，然而在表面電漿波平行介面方向上的傳播，其傳播長度可達到數十至數百個um等級，可大幅提升感測範圍，因而延伸出本研究以對稱介電質膜層結構設計(Long-range SPR)來改善檢測之敏感度並配合波導耦合方式研究側向表面電漿波的傳播行為及其傳播長度。 經本研究實驗結果，證實對稱介電質膜層結構設計確實能幫助表面電漿波的耦合，依待測物的不同選擇適當之介電質層，配合金膜厚度的控制可使欲感測之樣本有最佳的敏感度，介電質層的厚度必須小於漸逝波所能穿透之深度，以確保表面電漿共振現象得以產生。 由於研究之需要，本研究開發出自動化高解析度角度調變SPR影像系統，可取代原有之GWC SPR imager，系統操作方便，節省實驗時間，並可減少人為判讀誤差，系統角度調變之感測解析度可由1.14×10-3RIU提高至3.93×10-5RIU，強度調變之感測解析度由1.05×10-6RIU提升至4.66×10-7RIU。另外本研究嘗試提出一創新式波導耦合側向表面電漿波元件以研究側向表面電漿波的存在及波導耦合機制，配合對稱介電質膜層設計，期望將來能實做出一個生醫感測器。

Surface plasmon resonance (SPR) phenomenon has been used in optical sensors for decades. For traditional sensor applications, we often use 50 nm gold film for optimal SPR signal. However, In the range of visible light, the FWHM(Full Width Half Maximum) of SPR curve is about 4 to 6 degrees. To improve the sensor performance, we can work on reducing FWHM and increasing active sensing area by propagation length of SPR wave. In traditional approach, which uses the sensing ability of field depth in 100~200nm perpendicular to the interface between metal and dielectric. We use the traveling wave in the plane parallel to the interface of metal and dielectric to reach the propagation length of much longer distance. This research is to investigate a special layer design to improve detection sensitivity and integrate waveguide couple method to study lateral propagation of SPR. According to our research results, long-range SPR indeed help SPR coupling. By appropriate selection of dielectric material and metal thickness, we can enhance sensing ability in designed detecting range. Most important is that the thickness of dielectric layer have to be thinner than the depth evanescent wave can reach. We developed an automatic high resolution SPR angle modulation system, that can shorten experiment time and avoid manual’s error. The resolution can reach 3.93×10-5 RIU for angle modulation and 4.66×10-7 RIU for intensity modulation. Also, this research propose a novel waveguide coupling sensing chip of lateral propagation SPR. We hope to verify the existence of lateral propagation of SPR and understand the waveguide coupling mechanism. By applying the long-range SPR layer design, a sensitive biosensor can be realized in the future.