具金奈米粒子之蜂窩狀孔洞高分子薄膜基板應用於表面增強拉曼散射檢測

Abstract

本實驗成功開發一新型的表面增強拉曼散射基板(surface-enhanced Raman scattering substrates, SERS substrates)，因具有三維規則蜂窩狀孔洞結構，將可有效地改善拉曼訊號之偵測靈敏度及再現性，應用於快速檢測多種化合物。 此三維規則排列之蜂窩狀孔洞結構以polyurethane-co-azetidine-2,4-dione (PU-PAZ)作為材料，於呼吸法(breath figure method)的製備方式中，PU-PAZ高分子結構中的兩性型樹枝狀高分子能穩定水分子及高分子溶液間的界面，並控制水分子整齊排列於溶液表面或深入其中的自組裝現象，等到水分子及溶劑完全揮發即得到規整的孔洞結構。以不同相對濕度及高分子溶液濃度來調控孔洞大小及排列整齊度，再附著金奈米粒子製備出多層孔洞結構之SERS基板，與表面具金之平膜基板比較SERS放大效果。 基板的檢測靈敏度將以增強因子(enhancement factors, EF)來量化，計算具有孔洞結構SERS基板的EF值約為106，遠大於對照組的平膜SERS基板(平膜基板之EF值為104)。接著以不同深度的共軛焦拉曼光譜掃描及SEM圖像，佐證本實驗所推論於兩種結構的SERS放大機制差異，顯示多孔洞SERS基板因表面及三維孔洞結構中皆佈滿金奈米粒子，可由鄰近粒子間的熱點效應(hot-spots resonance effects)，大幅增強散射於金屬表面電磁場之待測物拉曼訊號；此外，雷射可於孔洞腔體進行多次反射，可增加被照射之金奈米粒子因表面電漿子共振(surface plasmon)產生熱點效應的機率，因此，三維孔洞基板同時有表面及孔洞內部加成的SERS訊號，故較二維平面之基板擁有較優良之SERS效應。 本實驗亦討論金奈米粒子的粒徑大小、孔洞結構之表面形貌等變因，對SERS基板檢測能力的影響，結果顯示粒徑較大之金奈米粒子可引發較強之熱點效應，能增進基板偵測靈敏度；而孔洞大小及排列規則度也對訊號偵測靈敏度及再現性扮演重要的因素。該SERS基板除了能快速放大極微量待測物的拉曼訊號以利檢測，亦可用於不同化合物分子的偵測，如在針對R6G分子的偵測極限濃度(Limitation of detection, LOD)可達到10-8 M，且找到濃度介於10-5至10-8 M的檢量線以利未來的應用。 關鍵字：表面增強拉曼散射、蜂窩狀孔洞結構、呼吸法、金奈米粒子、熱點效應

Novel surface-enhanced Raman scattering (SERS) substrates with three-dimensional (3D) porous structures have been developed for effectively improving the sensitivity and reproducibility of SERS, which can rapidly detect small molecules. Periodical arrays of the honeycomb-like substrates were fabricated by self-assembling polyurethane-co-azetidine-2,4-dione (PU-PAZ) polymers. PU-PAZ comprising amphiphilic dendrons could stabilize the interfaces between the water droplets and polymer solution, and then organize into regular porous structures through the breath figure method. Subsequently, SERS substrates were fabricated by immobilizing gold nanoparticles (AuNPs) onto the polymer films with various 3D honeycomb-like porous structures, controlled by different PU-PAZ concentrations and relative humidities. Results show that surface enhancement factors of honeycomb-like substrates as large as 106 are much higher than that of flat-film substrates (control group) due to enormous accumulation of hot-spots resonance effects in the 3D porous structure as verified through Raman mapping at various positions of the z-axis. Furthermore, the particle size effects were evaluated by immobilized different sizes of AuNPs on the honeycomb-like substrates, indicating larger AuNPs could induce more pronounced hot-spots effects as verified by the broad scattering peak of aggregating AuNPs. The generation of hot-spots resonance to enhance Raman intensity is strongly dependent on the diameter of AuNPs, the pore sizes and distributions of the 3D honeycomb-like porous substrates. Such substrates are ready for label-free and rapid SERS detection. Keywords：surface-enhanced Raman scattering (SERS); breath figure; honeycomb-like polymeric films; gold nanoparticles; hot-spots resonance effects.