軟模板合成鉑奈米中空球及其光學特性之感測應用

Abstract

本論文三大主題包括：(1) 三段塊式高分子合成Pt奈米中空球、(2) 分析與理論模擬Pt奈米中空球的光學特性、(3) Pt奈米中空球的光學感測應用。 在中空結構合成方面，一個簡單合成步驟的製程可以有效降低汙染並減省能源，此外，單一貴金屬成分則可以滿足各種特殊應用並使其結構及光譜特性單純化，而最重要的是要避免使用傳統合成中空結構常用之加凡尼取代法，以排除標準還原電位所造成之成分限制。在上述綠色合成政策的前提下，我們首次成功地在水溶液中，利用三段塊式高分子(PPO-PEO-PPO, Pluronic 25R4)作為軟模板，以NaBH4還原劑，在冰浴下合成出Pt奈米中空球。 當特定波長入射到介質中之金屬奈米粒子時，入射電磁場造成金屬表面自由電子共振，即為表面電漿共振(SPR)效應。此SPR現象可由金屬奈米粒子UV-visible光譜吸收峰來進行觀察。而吸收峰之波長及波形除了與金屬奈米粒子之成分、尺寸、及排列方式息息相關，亦易受粒子周遭介質介電性質之影響。從Pt奈米中空球之UV-visible光譜可以發現，吸收峰由Pt實心粒子之200 nm~250 nm大幅紅位移至400~500 nm，且從單一寬吸收峰明顯分解為三個吸收峰，從光譜模擬分析証據顯示，此波峰分解是由三個主要尺寸分佈所造成。Pt奈米中空球獨特之結構(尺寸)及環境(介電性質)高依存性光譜，可以作為SPR感測器之應用，直接偵測能與Pt產生各式鍵結之分析物，或是介質中含有分析物時，介質整體介電性質之微變化。本研究亦利用Pt奈米中空球特有的光學特性進行(葡萄醣)感測效果的測試。從實驗中發現，Pt吸收光譜的吸收峰強度會隨葡萄醣濃度的增加而逐漸下降，展示出Pt奈米中空球具有感測葡萄醣之潛力。

This thesis mainly explores three topics involving (1) tri-block-copolymer assisted synthesis of platinum nanoparticle assembled hollow spheres (Pt NSHS), (2) theoretical simulation of UV-visible extinction spectra of Pt NSHS and (3) applications of Pt NSHS for optical-based sensors (glucose). Under synthetic policies of facile routes for preventing pollutions and saving energies, sole noble element for satisfying specific applications and simplifying structural and optical properties, and more importantly non-galvanic replacement method for eliminating synthesis limitation regarding materials standard reduction potentials, we have successfully synthesized size-controlled Pt NSHS using tri-block copolymers of poly(propylene oxide)-poly(ethylene oxide) -poly(propylene oxide) (PPO-PEO-PPO, Pluronic 25R4) and sodium borohydride as soft-templates and reducing agents, respectively, in aqueous solutions. In contrast to the most commonly used method of galvanic replacement for the preparation of hollow nanostructures as frequently reported, to the best of our knowledge, the novel Pt NSHS are the first time to be synthesized by this unique and facile way which fulfills our green synthetic polices. The surface plasmon resonance (SPR), which exhibits obviously absorption band in the UV-visible spectrum, originates from a collective oscillation of the free electrons at the interface between the metallic nanostructures and the dielectric medium with the incident electromagnetic fields. The wavelength and profile of the absorption bands not only strongly depend on the composition, size, shape and pattern of the nanostructures, but are also extremely sensitive to the dielectric surrounding. It has been found that the absorption band shifts from 200 nm–250 nm of Pt solid spheres to 400 nm–500 nm of the present Pt NSHS and splits into three sharper bands mainly due to the existence of three different size distributions as proven with systematically theoretical calculations. The observed distinct structurally- and environmentally-dependent optical properties of the present Pt NSHS allow direct detection of analyte binding or slight dielectric change of medium containing analytes in real time as SPR based sensors. The glucose sensing properties of the Pt NSHS in aqueous solutions have also been demonstrated.