金屬奈米粒子陣列的組裝及其表面增強拉曼散射活性之研究

Abstract

金屬奈米粒子陣列在表面增強拉曼散射 (SERS) 領域具有諸多應用，例如：分析物微量檢測、醫學檢測等。拉曼訊號的增強主要是通過表面電漿共振耦合效應，使金屬奈米結構能產生更強的熱點效應，藉此提升分子的拉曼訊號。因此，如何設計出具備高 SERS 活性之基板受到廣泛關注。本研究中分別使用中孔洞二氧化矽奈米顆粒 (mesoporous silica nanoparticles, MSNs) 與中孔洞二氧化矽薄膜 (mesoporous silica thin film, MSTF) 作為模板，利用一種簡單、快速且不需要額外添加金屬形貌保護劑的合成方法，來製備尺寸均勻、排列規則緊密的金、銀奈米粒子陣列，並將其應用於拉曼訊號的增強上。主要研究內容如下: (1) 利用調變擴孔劑的種類合成出具有不同孔洞大小的中孔洞二氧化矽模板，通過模板的形貌調控從而控制所製備出的金奈米粒子陣列之顆粒大小與粒子間間距。為了探討基板之 SERS 效能，我們利用4-巰基苯甲酸 (4-mercaptobenzoic acid, 4-MBA) 作為探測分子。結果顯示，金奈米顆粒尺寸為 5.1 nm、粒子間間距為 1.9 nm 的 MSN-Au 基板具有最佳之 SERS 活性。通過優化實驗條件，基板對 4-MBA 分子的最低偵測極限低至 10-10 M，且具有良好的訊號均勻性 (訊號強度相對標準偏差為 12%) 和訊號穩定性，基板保存於室溫環境下三個月後仍能維持穩定高效的訊號強度。此外，將 MSN-Au_5 nm 基板應用至實際檢測果汁中與果皮上的農藥殘留，檢測極限低於法規標準的農藥濃度表現出顯著的 SERS 增強特性，於檢測微量農藥殘留方面具有極大的應用潛力。 (2) 利用硫代硫酸銀作為 Ag 前驅物製備出之銀奈米粒子陣列 (MSN-Ag_5 nm) 基板，結果顯示，銀奈米顆粒尺寸為 5 nm、粒子間間距為 1.9 nm。由 SERS 活性探討中顯示，銀基板局部表現出優於金奈米粒子陣列之顯著的 SERS 增強特性。然而，由於表面上之硫元素的殘留會影響到分子吸附至基板表面的過程，進而影響到基板之 SERS 效能表現，因此銀奈米粒子陣列基板之訊號均勻性還需進一步優化。

Metal nanoparticle arrays have been developed for various surface-enhanced Raman scattering applications, such as trace detection of analytes and medical-ingredients. The basic concept of the SERS effect is that the Raman scattering cross-section of molecules located in nanogaps among metallic nanostructures can be tremendously enhanced by the amplification of electromagnetic fields resulted from the excited localized surface plasmon resonances (LSPR). Herein, the extremely uniform-sized single-layer gold nanoparticle arrays and silver nanoparticle arrays embed in well-ordered mesoporous silica (MSNs and MSTF) on silicon wafer were fabricated via a surfactant-free method for SERS applications. The main research contents are as follow: (1) The MSNs and MSTF act as hosts to confine the size and uniformity of metal NPs. The pore size and nanogaps of metal NPs can be precisely controlled by tuning the pore size and pore to pore distance of MSNs and MSTF hosts. As a result, the MSN-Au_5 nm substrate achieved the outstanding SERS activities with an enhancement factor 2.8×108. Under the optimal conditions, this SERS substrate exhibited a low detection limit (10–10 M for 4-mercaptobenzoic) and excellent enhancement uniformity (relative standard deviation, RSD = 12%) and long-term storage stability for more than 3 months. Furthermore, the detection of the pesticide residue both in fruit juice and fruit peel showing the excellent SERS signals under the natural environment. These results indicate that MSN-Au_5 nm as a SERS substrate own great potential in the application of trace level pesticide detection. (2) MSN-Ag_5 nm substrate prepared by using silver thiosulfate as precursor. The results show that the residual sulfur on the surface of the substrate will affect the adsorption process of molecules to the substrate surface, and then affect the SERS performance of the substrate.