增強電漿子奈米結構的偵測靈敏度與分子結合效率之研究

Enhancing detection sensitivity and molecular binding rate in plasmonic nanostructures

林恩宏(En-Hung Lin)

指導教授 ： 李明昌 ； 魏培坤

國立清華大學/電機資訊學院/光電工程研究所/博士(2014年)

摘要

在本論文中提出了幾種方式來有效率的利用金屬週期結構提升表面電漿共振的偵測極限，方法分別是小角度入射樣品、光譜積分法以及結構本身的色散曲線，此外也利用了高密度的金屬圓盤矩陣結構，進行螢光分子的動態光捕捉研究。
在奈米狹縫的實驗中，金屬奈米狹縫陣列是利用奈米壓印技術製作而成，其狹縫寬度與週期分別是60奈米及500奈米，當光源小角度入射至奈米狹縫樣品時，會導引出表面模態與基板模態的共振耦合效應，此效應會在入射角度為5.5度時提高約2.24倍的強度靈敏度，另外在此角度入射樣品時會產生多重波峰，藉由利用多重波峰特性並結合光譜積分法的數值分析方式，與單光譜分析方式做比較，及提升訊噪比達5倍左右。
在奈米孔洞的實驗中，金屬奈米孔洞陣列是利用奈米壓印技術製作而成，其孔洞直徑與週期分別是180奈米及600奈米，在改變入射角度時，奈米孔洞的結構中會產生(±1,∓1)的表面模態，此模態有很高的角度靈敏度達到約440 deg/RIU，此一模態的產生，是由於大角度入射樣品造成電場侷限在孔洞腔體中，進而形成一平緩色散曲線，與接近0度入射相比，此一表面模態增加了約6.2倍的角度靈敏度，另外與傳統稜鏡耦合方式相比，在630奈米與850奈米的波長下，分別提升了約2.3以及4.5倍的角度靈敏度。
在高密度金屬奈米圓盤的實驗中，金屬奈米圓盤陣列是利用電子束微影技術製作而成，其圓盤直徑與週期分別是500奈米及1微米，利用暗場入射光(照射強度約3.58 × 103 W/m2)照射在此金屬圓盤上，其圓盤邊緣會有約15倍的螢光增強效果，也利用590奈米的塑膠小球實驗來證明此結構產生的光捕捉力量約10飛牛頓，此外在含有硫基鍵結與Cy5螢光染料的DNA分子動能實驗方面，也證明了在不同照射強度下，會有不同的鍵結效率，分別是2.14 × 103 s−1 (I = 0.7 × 103 W/m2)以及1.15 × 105 s−1 (I = 3.58 × 103 W/m2)。
根據上述提供的方式，並且結合小角度入射樣品、光譜積分法以及結構本身的色散曲線，可以有效率的提高強度、角度靈敏度以及偵測極限，此外利用金屬圓盤結構也可有效率的提高分子的鍵結效率並縮短鍵結時間。

關鍵字

表面電漿共振 ； 增強靈敏度 ； 奈米週期性結構 ； 電漿子光捕捉 ； 增強鍵結效率

並列摘要

In this dissertation, we report new methods to efficiently improve the detection limit of surface plasmon resonance in periodic metallic nanostructures by using small angle illumination, spectral integration analysis and dispersion curve of structure. We also present the dynamic study of optical trapping of fluorescent molecules using high-density gold nanodisk arrays.
In nanoslit structure, the large-area gold nanoslit arrays were fabricated by thermal-annealing template-stripping method. The slit width and period was 60nm and 500 nm. The small angle illumination induced a resonant coupling between surface plasmon mode and substrate mode. It increased ~2.24 times intensity sensitivity at 5.5° incident angle. The small-angle illumination also resulted in multiple resonant peaks. The spectral integration method integrated all changes near the resonant peaks and increased the signal to noise ratio about 5 times as compared to single-wavelength intensity analysis.
In nanohole structure, the large-area gold nanohole arrays were fabricated by thermal-annealing template-stripping method. The hole diameter and period was 180nm and 600nm. The (±1,∓1) surface mode which has higher angular RIU sensitivity of surface plasmon resonance improvement ~440 deg/RIU by change angle of light incident. The flat dispersion curve of (±1,∓1) surface mode was observed by large angle illumination due to electric field localized in hole cavity. It increased ~6.2 times than (±1,0) surface mode near 0° and also increased ~2.3 and ~4.5 times than prism coupler-based SPR sensor of angular RIU sensitivity at 630nm and 850nm, respectively.
In gold nanodisk strucutre, the gold nanodisks were fabricated by electron beam lithography with a diameter of 500 nm and a period of 1 μm. Dark-field illumination showed ∼15 times enhancement of fluorescence near edges of nanodisks. Such enhanced near-field generated an optical trapping force of ∼10 fN under 3.58 × 103 W/m2 illumination intensity as calculated from the Brownian motions of 590 nm polystyrene beads. Kinetic observation of thiolated DNA modified with Cy5 dye showed different binding rates of DNA under different illumination intensity. The binding rate increased from 2.14 × 103 s−1 (I = 0.7 × 103 W/m2) to 1.15 × 105 s−1 (I = 3.58 × 103 W/m2).
Based on above methods, it efficiently improves the intensity and angular sensitivity of surface plasmon resonance such as small angle incidence, spectral integration and dispersion curve of strucutre. Furthermore, gold nanodisks also efficiently improve both detection limit and interaction time.

並列關鍵字

surface plasmon resonance ； enhance sensitivity ； metal periodic structure ； plasmonic optical trapping ； enhance binding efficiency

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