微奈米結構用於具超高靈敏度與定量分析能力之表面增強拉曼散射基材之研究

Abstract

本論文以不同的基材製備表面增強拉曼散射基板，並利用高密度的熱點分佈搭配適當的量測架構，開發出高靈敏度、低成本且環境友善之表面增強拉曼散射基板。在本論文第一部分與第二部分中，我們分別以雷射熱退火產生之光熱效應與稀釋奈米銀膠的塗佈，製備具有高密度分佈的銀奈米粒子於濾紙與矽基材表面，利用銀奈米粒子間奈米尺寸等級的間距所產生之耦合效應增強電場，作低濃度與定量分析之研究，並進一步探討此基材之穩定性。實驗結果得到線性響應區達到10-11M~10-4M於4-胺基苯硫酚(4-ATP)的濃度範圍，與羅丹明(R6G)分子在濃度10-12~10-3M的線性區範圍，在極低濃度時進一步將訊號得到之機率的因素考慮進去後，在更低濃度取其拉曼訊號強度平均值，更可將線性區範圍擴大至10-18~10-3M。此外，本論文也於穩定性實驗找到較不易受氧化影響的銀奈米顆粒尺寸；並藉由足夠多的熱點分佈得到趨近於階梯狀訊號變化之羅丹明數個分子檢測訊號。 本論文的第三部分，我們利用鋁箔紙與棉花棒作為準三維結構軟式基材，塗佈以密集之奈米銀膠後作羅丹明檢測極限實驗，成功地利用鋁箔紙基材達到羅丹明在633nm雷射光源下於濃度10-18M的拉曼訊號量測極限，甚至在785nm雷射光源下達到濃度10-9M的檢測極限。不僅有效利用鋁箔紙與棉花棒方便取得與使用的特性，製造出簡單、拋棄式且訊號增益極高的拉曼基材。 論文第四部份探討在一維的V型溝槽結構上，改變入射雷射光波長、結構尺寸、偏振方向、金屬種類、薄膜披覆形貌與物鏡倍率等量測架構。並評估上述變因對此V型溝槽結構之拉曼量測訊號的影響。更進一步利用三維有限時域差分法模擬上述變因之效應。實驗結果發現由表面電漿效應加上週期性V型溝槽結構的侷限效應，銀平膜披覆於V型溝槽的最低羅丹明檢測極限可達10-12M之低濃度；並透過改變物鏡倍率與雷射光源波長，探討對應的最佳量測架構。並分析有效拉曼偵測待測物體積對偵測濃度極限的影響。

In this thesis, we used several conventional substrates to develop low-cost, highly sensitive and eco-friendly surface enhanced Raman scattering (SERS) substrates. The substrates also performed superior quantitative ability under ultralow concentration of analyte molecules. In the first part of the thesis, we adopted laser-induced photo-thermal effect to convert silver (Ag) thin film into Ag nanoparticles (AgNPs) on filter paper. And then superhydrophobic treatment of coating perflurooctyltrichlorosilane onto the paper based SERS substrates was applied to further improve SERS detection sensitivity. By using the excitation laser having a wavelength of 633 nm, the AgNPs SERS paper provided linear response of SERS intensity of the concentration of 4-aminothiophenol (4-ATP) from 10-4 M to 10-11 M in log/log plot, and the detection limit was 10-13 M. Ag paste is generally used for the preparation of electrode of solar cells. In the second part of thesis, we used Ag nanopaste and hexane to coat extremely close-packed AgNPs on silicon (Si) substrates. The localized surface plasmon resonance (LSPR) and coupling effects of Ag nanopaste based SERS substrates make the detection limit of rhodamine (R6G) could down to 10-18 M. Moreover, the Ag nanopaste based substrates could perform linear response of SERS signals in measuring R6G samples with the concentration from 10-3 M to 10-12 M in log/log plot. Moreover, we could further obtain a larger linear response region form 10-3 M to 10-18 M by including the probability factor that signals of very low concentration samples could be detected. Furthermore, we investigated the size effect of AgNPs on surface oxidation phenomenon for study the stability of AgNPs based SERS substrates. In the third part of the thesis, we used Ag nanopaste coated aluminum foil and cotton swab as the flexible and quasi-3D SERS structures. The Ag nanopaste coated aluminum foil and cotton swab based SERS substrates are convenient, inexpensive, eco-friendly, portable and highly sensitive. By detecting the Raman signal of R6G samples, the aluminum foil based substrate performed the detection limit down to 10-18 M and 10-9 M under excitation lasers having a wavelength of 633nm and 785nm, respectively. In the fourth part of the thesis, the potassium hydroxide based anisotropic etching process was used to fabricate one-dimensional Si V-groove structure, then different metal thin films were deposited onto the V-groove structure. We studied the SERS effect of the V-groove structure by changing the wavelength of excitation laser, polarization, morphology of metal film, and depth of focus of the measurement setup. We also used the three-dimensional finite-difference time domain (3D-FDTD) method to simulate the electric field enhancement effects on dimension of the V-groove structures, thickness and morphology of different kinds of metal films. With the advantages of SPR and cavity effects, flat Ag film coated V-groove structure could perform the detection limit on rhodamine 6G samples at the concentration of 10-12 M.