金奈米棒表面電漿共振長軸特徵波帶之界面環境效應暨應用於光柵式導模共振生物感測器新機制之開發

The Interfacial Effect of the Gold Nanorod on its Longitudinal Surface Plasma Resonance & the Development of New Biosensing Mechanism in Guided-mode Resonance

吳侑勳(Yu-Hsun Wu)

指導教授 ： 王崇人

國立中正大學/理學院/化學暨生物化學系/碩士(2015年)

摘要

本論文分為兩部分。第一部分，在改變介電常數之有效界面環境範圍內，探討金奈米棒（AuNR）表面電漿共振長軸特徵波帶（SPRlong）對於界面環境變化的靈敏度；第二部分則是應用金奈米棒於光柵式導模共振（Guided-mode resonance; GMR）生物感測器，藉由AuNR的光學特性開發新的逆轉訊號之GMR感測機制，並增強其靈敏度。
我們在第一部分嘗試回答一個問題：在AuNR兩端與側邊界面周圍的介電常數變化對SPRlong的貢獻是否相同?我們曾透過溶膠-凝膠法開發金奈米棒-二氧化矽（AuNR-SiO2）核殼奈米粒子，並操控殼層結構形成均勻（AuNR-uSiO2）及不均勻殼層（AuNR-nuSiO2）。因為SiO2的生成，使有效界面環境範圍內的介電常數上升，造成SPRlong紅位移。根據我們的測量結果，側邊厚度（ST）對於SPRlong位移的貢獻可能大於兩端厚度（ET）。在此我們提出一系列對於SPRlong位移的探討，並藉由以下兩種不同方法控制界面環境的介電常數：操控SiO2殼層厚度與緻密度。結果顯示在AuNR-nuSiO2系統下，當ST約5 nm且ET約0 nm時，SPRlong幾乎維持不變；ST大於5 nm後，SPRlong會隨著ET緩慢成長而位移，由此清楚說明AuNR兩端之界面環境為主要影響SPRlong之因素。接著我們採用兩種不同策略達到殼層緻密度的操控：不同種類的前驅物以及前驅物濃度，兩者皆能改變殼層的成長速率與緻密度。我們選擇MPTMS (3-mercaptopropyl trimethoxysilane) 與 TEOS (tetraethyl orthosilicate) 兩種作為前驅物。其中一項成果是開發一合成方法，以TEOS為前驅物合成AuNR-nuSiO2，而在過去的文獻中沒有提及。實驗證實前驅物濃度越高，SiO2殼層緻密度越小，SPRlong位移也會隨之減少，且兩端界面環境影響SPRlong之轉折點從ST等於5.2 nm改變至7.7 nm。另外，在TEOS系統中SPRlong的位移小於MPTMS系統，兩者差異可藉由比表面積及孔洞分析儀（ASPS/BET）檢測結果證實。數據顯示TEOS合成的SiO2殼層之總表面積為106.11 m2/g，明顯大於MPTM合成的SiO2殼層之總表面積，其值約1.27 m2/g。
第二部分新感測機制之研究主要分為兩個階段：首先，在玻璃表面以旋轉塗佈法製作凝膠層，利用壓印法使凝膠層形成週期性結構，最後於週期性結構表面濺鍍厚度為70 nm的二氧化鈦，即完成GMR生物感測器之波導層與光柵；第二是在其表面修飾分子（MPDMS），利用金硫鍵結將AuNR固定於GMR生物感測器之光柵表面，接著在AuNR表面修飾生物抗體（biotin），並調控SPRlong與GMR的共振頻率相符（約885 nm）。在第一階段，因波導層折射率大於玻璃與環境，且光柵具有固定週期（555 nm），當入射光經過光柵產生繞射，並使特定波長於波導層進行全反射，即為導模共振現象。在生物感測方面，利用特定蛋白質（Streptavidin）與biotin結合，因AuNR周圍環境的改變，造成SPRlong位移且造成吸收值下降，當入射光的穿透與反射增加，使訊號強度增強，有別於先前研究利用金奈米球結合生物感測器之研究，模擬系統預測結果是AuNR的增強幅度約為金奈米球的2.5倍，而實驗結果則是增強約6倍。

關鍵字

表面電漿共振 ； 金奈米

並列摘要

This thesis is composed of two subjects which are both related to biosensing in gold nanorod (AuNR) system. In part I, we explored the sensitivity in the dependence of the longitudinal surface plasma resonance (SPRlong) of the AuNR on the dielectric constant of the effective interfacial surrounding medium. In part II, we applied AuNR system to the existing guided-mode resonance (GMR) biosensor for the purpose of enhancement in its detection limit.
We made the first attempt in part I to answer a question: Does the SPRlong depend equally or differently on the dielectric constant variation of the interfacial region either at the side or at the ends of the nanorod? We have previously developed synthetic routes to prepare AuNR-SiO2 core-shell nanoparticles via sol-gel process in fashions of either uniform thickness coating, AuNR-uSiO2, or non-uniform coating, AuNR-nuSiO2. The coating at the effective interfacial region causes the SPRlong shifts to the red due to the dielectric constant increase at the interfacial region. Our previous measurements implied that the thickness of the SiO2 at the side (ST) of nanorod contributing to the shift more than the thickness at the ends (ET). We present herein a series of SPRlong shift studies based on the control of interfacial dielectric constant by two different ways: the thickness and the porosities of the SiO2 shell. Our results showed in the AuNR-nuSiO2 system that the SPRlong remained nearly constant while the ST increased to ca. 5 nm and ET remained not visualized under TEM analysis. The SPRlong started shift while ST grew beyond 5 nm and ET increased very slowly. They clearly indicated that the contribution to the SPRlong shift comes from the interfacial variation at the rod ends. As for the series of studies for the control in SiO2 porosity, we adopted two different strategies: the types of the precursors for the sol-gel process and their concentrations. Both of them varies the coating rates and consequently the porosity. MPTMS (3-mercaptopropyl trimethoxysilane) and TEOS (tetraethyl orthosilicate) were chosen as the precursors. One of my achievements was to develop a way to synthesize AuNR-nuSiO2 by the use of the precursor TEOS. It was not found in literature. Our results showed that the higher the precursor concentration, the smaller in porosity the SiO2 shell became. The SPRlong shift from ET becamed smaller in the cases with lower precursor concentration that measured by the turning point of ST from 5.2 nm to 7.7 nm. Also, the SPRlong shifts much less in TEOS system than in MPTMS system. This difference was verified by the measurements from the surface area and porosimetry analyser (ASPS/BET). The total surface area of the SiO2 shell was measured to give 106.11 m2/g for the case of TEOS, which was much larger than that the case of MPTMS, 1.27 m2/g.
In part II, the synthesis of biosensor is divided into several steps:A biosensor structure consists of (i) a waveguide and a periodic structure (grating layer) are coated with the sol-gel layer on glass by spin coating; (ii) form the periodic structure on the layer through imprinting process; (iii) coat titanium dioxide thickness is 70 nm on the surface of the periodic structure; (iv) modify the grating layer by 3-mercaptopropylmethyldimethoxysilane (MPDMS), to fix AuNR on the layer by Au-S bonding; (v) modify AuNR surface with biotin, further tuned the resonance wavelength of AuNR and GMR are 885 nm. Because refractive index of waveguide is more than the glass and surrounding medium, and the period of grating layer is fixed (555 nm), when the incident light into waveguide, the propagating leaky waves couple to evanescent diffracted that form a standing wave within the waveguide surface yields a specific resonance wavelength and utilizing multiple total internal reflections along the waveguide, is known as “guided-mode resonance”. In the sensing test, we made the variation of interfacial region by streptavidin conjugate biotin that caused SPRlong shifts and reduced absorption. In contrast, the transmittance increating enhanced the signal. Compared to the previous system by gold nanosphere, the enhancement of new system is 2.5 times by simulation, and 6 times by the experimental result.

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