以銀奈米粒子聚集之週期性孔隙圓盤結構於表面增強拉曼散射光譜的應用

Abstract

本研究利用斷鍵-成核-長晶法來製備鑲嵌於聚苯乙烯球陣列表面的銀奈米粒子，再藉由二氯甲烷移除聚苯乙烯球以形成由銀奈米粒子聚集成之孔隙圓盤結構，並應用於表面增強拉曼散射光譜 (Surface-enhanced Raman scattering, SERS) 效應的研究。相較於銀奈米粒子鑲嵌在聚苯乙烯球陣列表面的結構，由銀奈米粒子聚集成之圓盤孔洞結構具有更多的SERS熱點數目，可有效提升SERS的訊號強度及偵測極限。 實驗中探討的變因包括：還原劑的酸鹼值、前驅物溶液浸泡時間、銀奈米粒子粒徑、銀奈米粒子排列密度，以及圓盤形貌對SERS訊號強度的影響。在最佳實驗條件下，鑲嵌於聚苯乙烯球表面之粒徑大小約為120 nm的銀奈米粒子可因聚苯乙烯球被二氯甲烷溶解之效應，堆疊出高度約為0.22 μm、直徑約為1 μm之週期性銀奈米粒子聚集孔隙圓盤。 使用羅丹明6G (Rhodamine 6G, R6G) 作為SERS偵測之分析物進行測試，發現在最佳的SERS增強效果中所得之增強因子 (Enhancement factor, EF) 可達約1012 倍，而R6G分子之偵測極限可低至10-11 M。同時在R6G低濃度實驗 (10-7 - 10-10 M) 中發現於611 cm-1 訊號處之強度值與R6G莫耳濃度之對數值呈現高度線性關係(R2 = 0.98)，此基材亦可應用於偵測非類固醇消炎藥可多普洛菲 (Ketoprofen)，並得到偵測極限為10-9 M。

Silver nanoparticle-aggregated periodic porous pancake structures act as a sensitive substrate for surface-enhanced Raman scattering (SERS) with a large enhancement factor and a low limit of detection for Rhodamine 6G. In the fabrication process, silver nanoparticles are synthesized on hexagonal close-packed polystyrene microspheres through the Break-Seed-Growth method. After the removal of polystyrene spheres, surface decorated silver nanoparticles aggregate into a periodic porous pancake structure. This unique structure creates more SERS hot spots and enhances the SERS signal compared to the original silver nanoparticle decorated polystyrene sphere structure. The SERS enhancement is highly dependent upon the silver nanoparticle distribution and the pancake structure morphology. The silver nanoparticle size and distribution density can be controlled by the reducing agent solution pH value. Meanwhile, different periodic porous pancake structures are generated when the polystyrene arrays are immersed in dichloromethane with different polymer removal time. Under the optimized experimental condition, the 120 nm silver nanoparticle-aggregated periodic porous pancake renders a 1 μm diameter with 0.22 μm height structure. This structure delivers an enhancement factor of 1012 and an extremely low 10-11 M detection limit for Rhodamine 6G. A linear range between 10-7 - 10-10 M is also found with R2 = 0.98 when the 611 cm-1 signal is monitored. This structure also can be applied for detection of Ketoprofen, reaching the concentration as low as 10-9 M.