光波在週期性奈米金屬結構之特性與其在生醫感測之應用

The Properties of Optical Wave in Periodic Metallic Nanostructures and Its Application in Biosensing

李光立(Kuang-Li Lee)

指導教授 ： 王維新

國立臺灣大學/電機資訊學院/光電工程學研究所/博士(2008年)

https://doi.org/10.6342/NTU.2008.01734

摘要

本論文探討光波在奈米金屬單狹縫與週期性狹縫的光學特性，並且利用表面電漿子共振與夾縫電漿子共振製作出高靈敏度、免標定、高通量、晶片型態與可重複使用的新穎生物感測器，其單元檢測面積為100µm×100µm。在奈米金屬狹縫光學特性的研究中，利用電子束微影術及反應式離子蝕刻術在100 nm-200 nm金膜上製作週期400 nm-900 nm、狹縫寬度20 nm-200 nm的奈米金屬結構。實驗結果顯示，存在於狹縫中的夾縫電漿子共振在穿透光譜上呈現一半高寬較大的波峰，波峰位置受狹縫寬度及厚度影響；存在於狹縫外的表面電漿子共振對於光的穿透扮演著負面的角色，並在光譜上呈現一波谷。此外伴隨著波谷出現的波峰滿足Rayleigh異常現象的預測。這些波峰與波谷都會隨著環境折射率的改變而位移，因此可以應用於生物或化學檢測。在生物檢測的應用上，表面電漿子共振在水溶液環境中的折射率靈敏度達740 nm/RIU，同時對生物分子具有極佳的表面靈敏度。在比較表面電漿子與夾縫電漿子靈敏度的實驗中，由二氧化矽薄膜與醣體的檢測顯示夾縫電漿子有較佳的檢測能力，倘若光譜儀的解析度是0.1 nm，夾縫電漿子可以測得0.05 nm厚的二氧化矽薄膜厚度變化與分子量為4的生物分子。此外，夾縫電漿子的靈敏度與狹縫寬度有關，當狹縫由100 nm縮減至30 nm時，夾縫電漿子的靈敏度增加10倍，同時也高出表面電漿子的靈敏度約一個數量級。在檢測直徑為13 nm的奈米金球實驗中，夾縫電漿子在低奈米金球密度下的顆粒偵測靈敏度大約是表面電漿子的3倍。倘若光譜儀的解析度達0.1 nm或者燈源的強度穩定度達0.2%，夾縫電漿子的偵測靈敏度可達每平方微米一個粒子，此偵測能力與應用在DNA陣列檢測的螢光標定法的靈敏度每平方微米約0.5個螢光分子相當接近。因此，週期性奈米金屬狹縫可與奈米金屬顆粒標定法結合，以提升感測器的偵測極限，並應用於DNA及蛋白質陣列檢測。推測夾縫電漿子具有較佳靈敏度的可能原因是狹縫內的生物分子或奈米金球與夾縫電漿子具有較大的重疊積分。

關鍵字

光學生物感測器 ； 夾縫電漿子 ； 表面電漿子共振 ； 奈米結構 ； 奈米金屬狹縫 ； 空腔膜態

並列摘要

In this dissertation, a detailed study of the optical properties of single metallic nanoslit and multiple metallic nanoslits is presented. In experiment, high sensitive, label-free, high-throughput, reusable, and chip-based biosensor arrays based on surface and gap plasmon resonance were fabricated and tested. In the study of optical properties of metallic nanostructures, metallic nanoslits with periods varying from 400 to 900 nm and widths ranging from 20 to 200 nm were fabricated on a thin gold film using e-beam lithography and reactive ion etching. The thickness of the gold film is varying from 100 to 200 nm and the area of the metallic nanoslit array is chosen as 100 µm×100 µm. Experimental results show that gap plasmon resonance in the slit generates a peak with a broader full-width half-maximum in the transmission spectrum and the peak wavelength is affected by slit width and film thickness. That’s due to surface plasmon resonances outside the slit play a negative role in optical transmission and present a dip in the transmission spectrum. Besides, a peak accompanying an SPR dip can be predicted by Rayleight anomaly. The peaks or dip is sensitive to the refractive index change of the environment and can be applied in biological or chemical sensing. In the application of biological detection, SPR biosensor achieved a detection sensitivity of up to 740 nm per refractive index unit and an antigen–antibody interaction experiment in an aqueous environment verified the sensitivity in a surface binding event. The surface sensitivities of surface and gap plasmons were compared by coating a thin SiO2 film and different biomolecules on the nanoslit arrays. Experimental results show gap plasmons are more sensitive than conventional surface plasmons. The gap plasmons can detect a 0.05 nm-thick SiO2 film and ~4 Da-sized biomolecules attached to the surface when the resolution of a spectrometer is 0.1 nm. Besides, its detection sensitivity is increased with the decrease of the slit width. The gap plasmon is one order of magnitude more sensitive than the surface plasmon for slit widths smaller than 30 nm. In the 13-nm-diameter gold nanoparticle detection, gap plasmon is 3 times more sensitive than surface plasmon. A detection sensitivity of 1 particle/µm2 was achieved with a 0.1 nm wavelength shift or a 0.2% peak intensity change. This sensitivity is comparable with that of the fluorescent dyes ~0.5 fluors/µm2 used in DNA microarrays. Such a high sensitivity is attributed to the large overlap between biomolecules or nanoparticles and nanometer-sized gap plasmons.

並列關鍵字

Optical biosensors ； gap plasmons ； surface plasmon resonance ； nanostructures ； metallic nanoslits ； cavity mode

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