近年來，非破壞性光譜已普遍運用在諸多領域上，如生物體內顯影、生醫檢測、重金屬與農藥殘留檢測以及反應即時監測等。金屬奈米粒子獨特的局部表面電漿共振效應，常作為表面增強拉曼散射技術的主要增強來源。金與銀的核殼奈米粒子的局部表面電漿共振表現會隨著結構、核殼比例及形狀等因素而改變，其在催化、顯影、分析等相關領域上也受到相當大的注目。近年已有數篇文獻證實，金銀的核殼奈米粒子能夠得到比單一的金屬奈米粒子（金和銀）更出色的增強表現。為了得到這個獨特的材料，傳統濕式化學晶種法是最常被使用的合成手段，然而這個仍存在耗時、製程複雜及需要大量的化學藥劑等缺點。
本論文的研究目的在於開發簡單合成金核銀殼奈米粒子的技術並研究其在表面增強拉曼散射的表現。在本研究中，我們透過大氣常壓微電漿與液相反應進行金屬奈米粒子的合成。微電漿為至少一幾何維度小於一毫米的電漿，是一種氣體放電型態，能穩定存在於大氣常壓的環境，利於與水溶液電極反應。在不含化學還原劑的環境，微電漿內形成的能量物種能驅動溶液內的電化學反應以及匯聚粒子，我們將此方法進一步延伸到複合兩種金屬的合成。最後，藉由兩步驟大氣常壓微電漿與液相反應，在數分鐘內我們便能取得金核銀殼奈米粒子。與傳統濕式化學法所合成的雙金屬奈米粒子進行比較，發現透過大氣常壓微電漿進行合成，可以得到更均勻貼附在金表面的銀奈米殼層。實驗中所合成的材料會經過紫外光光譜、穿透式電子顯微鏡、掃描式電子顯微鏡、拉曼光譜以及X光繞射分析儀。
進一步將所得的材料進行有系統的表面增強拉曼散射研究，我們以羅丹明6G作為偵測分子，使用的雷射光波長為532 nm。我們發現金核銀殼雙金屬奈米粒子在特定比例下的增強表現優於單一的金、銀奈米粒子且對羅丹明6G分子的偵測極限達到10^-13莫爾濃度。相較於其他使用相同結構之文獻，我們的材料不但能用相對短的時間進行合成，且為極敏感的表面增強拉曼光譜的基材。此外，我們也針對以下幾點進行分析：（１）金核銀殼在微電漿系統下的合成機制。（２）電子在核殼結構中的轉移對表面增強拉曼散射強度的影響。
最後，為了測試我們材料應用於生物領域的可行性，我們針對生物分子「葉酸」進行偵測。葉酸是人體內重要的維他命B，醫學研究指出當葉酸分子低於10^-8莫爾濃度，身體會有健康上的疑慮。將葉酸做為探測分子進行表面增強拉曼散射的研究，發現當金核銀殼雙金屬奈米粒子作為基材，對葉酸分子的偵測極限可以達到10^-9莫爾濃度，顯示此材料在生醫分子感測應用上具有應用的潛力。

Surface-enhanced Raman scattering (SERS) is a non-destructive technology for various applications including in vivo imaging, biosensing, heavy metal or pesticide residues and in situ monitoring. Metal nanoparticles have been widely investigated in SERS applications due to their unique localized surface plasmonic resonance (LSPR). Au/Ag core-shell nanoparticles (Au@Ag NPs) allow it to tune their LSPR by varying the size and shape of the core or thickness of the shell and even producing stronger SERS activity in comparison with monometallic Au and Ag NPs. Therefore, they have attracted a lot of attention recently. To synthesize this attracted material, seed-mediated growth is the most widely used method. However, this conventional approach is usually time-consuming and laborious.
In our report, we present a facile synthesis of citrate-capped Au@Ag bimetallic nanoparticles using a novel atmospheric-pressure microplasma-assisted electrochemistry. Microplasmas are defined as gaseous discharges formed in electrode geometries where at least one dimension is less than 1mm. Due to surface volume change, microplasmas can be operated stably with an aqueous solution as an electrode at atmospheric pressure. Energetic species formed in the microplasma can initiate electrochemical reactions and nucleate nanoparticles in solution without chemical reducing agents. In our results, we synthesize Au@Ag core-shell bimetallic NPs in a minute time scale microplasma system. In comparison to seed-mediated growth, microplasma system not only can constitute Au@Ag NPs but also make the Ag shell form on the Au surface more homogeneous. As-produced samples are characterized by UV-vis, TEM, XRD, and Raman.
We further systematically study the SERS performance of Au@Ag NPs substrate and Au@Ag core-shell bimetallic nanostructure, which shows superior enhancement of SERS activity than Au, Ag NPs. The limit of detection of R6G molecules can be as low as 100 fM and high enhancement factor of 1.36 x 1011. It allows the SERS detection at single molecule level in R6G analysis. We further systematically study of: (1) the possible mechanism of Au@Ag NPs formation in two-step microplasma process. (2) The reasons why Au@Ag20 core-shell NPs can present the ultrasensitive SERS performance. In addition, for the purpose of bio-molecule sensing, we demonstrate the feasibility of using Au@Ag20 NPs as the SERS substrate for detecting the folic acid (FA) molecule. The result shows that the limit of detection of FA can achieve 1 nanomolar-level detection and that has great potential for biomolecular sensing.

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