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  • 學位論文

增進(侷域性)表面電漿共振感測器在強度、波長、 相位偵測法中靈敏度之研究

Enhancing Sensing Resolution of (Localized) Surface Plasmon Resonance Sensors Implemented by Intensity, Wavelength, and Phase Interrogations

指導教授 : 嚴大任

摘要


表面電漿共振為存在於金屬及介電層交界面上自由電子的集體震盪行為。由於此一共振條件為金屬及介電層之折射係數所左右,因此可利用其共振條件改變來判斷介電層之折射係數是否產生變化。更進一步來說,介電層上數十以至數百奈米的深度若有折射係數變化,便會反映在表面電漿子共振條件的改變上。考量到現今偵測系統的解析度,一般表面電漿共振所能測得的折射係數變化可輕易得達到10-6以上,因此表面電漿共振能在不需標定的情況下,立即的反映出生物分子接合的狀況。然而,對於更微量的偵測、更快速準確的檢定、更多樣性的功能、或是更低成本的追求始終是各感測平台極力企及的目標。因而在眾多研究者的努力至今,表面電漿共振感測器發展出不同的偵測方式以提供不同感測的需求。其中最常見的四種偵測方式為:角度、波長、強度、及相位偵測。 本研究關注在表面電漿共振感測器於不同偵測方式的靈敏度提昇及其潛在應用,以期能再進一步拓展表面電漿共振的應用範疇。例如,對於強度偵測此種不需複雜光路設計的高效率且廣泛應用的偵測平台,我們釐清其靈敏度與感測金屬層厚度的關係,進而推導出一條適合不同強度偵測系統的靈敏度預測公式。除此之外,我們發現靈敏度最大值的金屬厚度與一般熟知的最佳耦合金屬厚度有所落差,而此落差能由表面電漿共振的兩種損耗因子來解釋。對於相位偵測此種靈敏度極高的偵測平台,我們將之應用在侷域性表面電漿共振的量測上。侷域性表面電漿共振擁有不需耦合便能產生共振、奈米級尺度、共振型態多變等優勢,卻因靈敏度不足而有所缺憾。我們一改先前研究者在不同共振模態上的追求,利用相位偵測取代現有的波長偵測來增進其靈敏度。結果顯示,在消散波激發的情況下,相同結構的侷域性表面電漿共振能有超過八十倍的靈敏度提昇。此一研究除了證實相位偵測在侷域性表面電漿共振上的可行性之外,更補足其在靈敏度上的不足。對於波長偵測此種低成本且感測線性區大的偵測平台,我們希望能將其導入重點照護檢驗的應用上。利用銀/金雙層金屬薄膜代替常用的金膜,可以在不犧牲感測線性區的前提之下提昇約兩倍的靈敏度。此外我們更進一步改良波長偵測平台,以直接觀察反射光顏色變化代替比較共振波長變化。若然,銀/金雙層金屬薄膜在反射光顏色變化上比常用金膜能有十倍的靈敏度提昇。簡言之,我們希望藉由此篇論文研究,對於表面電漿共振感測器在不同偵測方式的應用中能有所幫助。

並列摘要


Surface plasmon resonance (SPR) is the collective oscillation of free electrons at the interface between metal and dielectric layers. Since the resonant condition of SPR is dominated by refractive indices of metal and dielectric layer, it is possible to distinguish the refractive index change of dielectric layer through the shifts of resonant condition. Considering the system resolution of SPR system nowadays, the sensing resolution up to 10-6 RIU (refractive index change) is available for a general SPR system. Accordingly, SPR provides a label-free platform to detect bio-interactions. However, for pursuing trace measurement, rapid detection, precise diagnosis, versatile functions, or lower cost, researchers devote themselves to develop different interrogations for diverse applications. For the most general four interrogations: angle, wavelength, intensity, and phase are well applied in current literatures. In this study, we focus on the sensitivity enhancement and potential applications of SPR interrogated by different routes, in order to expend its applying fields. For the non-complicated and efficient sensing platform, intensity interrogation, we discussed the relation between sensitivity and thickness of metal sensing layer, and further derived a generalized sensitivity model for intensity interrogation SPR system. In addition, we found that the optimized metal thickness in intensity interrogation is different from the thickness for best coupling efficiency, which is the most commonly used in research. This difference can be explained through two damping factors in SPR. For the sophisticated and ultra-sensitive sensing platform, phase interrogation, we applied such interrogation on LSPR. LSPR is characterized by coupler-free excitation, nano-scale, and diverse resonant modes; nevertheless, its sensitivity is over 10 folds lower than SPR. In contrast with other researchers who modified the resonant modes, we used phase interrogation instead of extinction spectra to enhance the sensitivity. Our results show that the sensitivity was enhanced over 80 folds at the same LSPR structures under the near-field excitation. This study not only confirms the feasibility of exploiting LSPR by optical phase, but also complements its insufficiency on sensitivity. For the low-cost and large linear detection range sensing platform, wavelength interrogation, we expect to have the potential application on point-of-care test. We proposed a color SPR system based on wavelength interrogation, in which we directly observed the color change of reflection rather than identified the resonant wavelength through spectrometer. Moreover, by using Ag/Au bi-metallic film to replace the general used Au film, we are able to enhance the sensitivity and color contrast without losing linear detection range. In short, we hope to promote SPR sensing system through the studies on intensity, phase, and wavelength interrogations.

參考文獻


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