Rao V Kesava, Radhakrishnan T P
School of Chemistry, University of Hyderabad, Hyderabad 500 046, India.
ACS Appl Mater Interfaces. 2015 Jun 17;7(23):12767-73. doi: 10.1021/acsami.5b04180. Epub 2015 Jun 2.
Development of facile routes to the fabrication of thin film substrates with tunable surface enhanced Raman scattering (SERS) efficiency and identification of the optimal conditions for maximizing the enhancement factor (EF) are significant in terms of both fundamental and application aspects of SERS. In the present work, polymer thin films with embedded bimetallic nanoparticles of Ag-Au are fabricated by a simple two-stage protocol. Ag nanoparticles are formed in the first stage, by the in situ reduction of silver nitrate by the poly(vinyl alcohol) (PVA) film through mild thermal annealing, without any additional reducing agent. In the second stage, aqueous solutions of chloroauric acid spread on the Ag-PVA thin film under ambient conditions, lead to the galvanic displacement of Ag by Au in situ inside the film, and the formation of Ag-Au particles. Evolution of the morphology of the bimetallic nanoparticles into hollow cage structures and the distribution of Au on the nanoparticles are revealed through electron microscopy and energy dispersive X-ray spectroscopy. The localized surface plasmon resonance (LSPR) extinction of the nanocomposite thin film evolves with the Ag-Au composition; theoretical simulation of the extinction spectra provides insight into the observed trends. The Ag-Au-PVA thin films are found to be efficient substrates for SERS. The EF follows the variation of the LSPR extinction vis-à-vis the excitation laser wavelength, but with an offset, and the maximum SERS effect is obtained at very low Au content; experiments with Rhodamine 6G showed EFs on the order of 10(8) and a limit of detection of 0.6 pmol. The present study describes a facile and simple fabrication of a nanocomposite thin film that can be conveniently deployed in SERS investigations, and the utility of the bimetallic system to tune and maximize the EF.
开发具有可调表面增强拉曼散射（SERS）效率的薄膜基底的简便制备方法，以及确定使增强因子（EF）最大化的最佳条件，在SERS的基础研究和应用方面都具有重要意义。在本工作中，通过一种简单的两步法制备了嵌入Ag-Au双金属纳米粒子的聚合物薄膜。在第一阶段，通过聚乙烯醇（PVA）薄膜在温和热退火条件下原位还原硝酸银形成Ag纳米粒子，无需任何额外的还原剂。在第二阶段，氯金酸水溶液在环境条件下铺展在Ag-PVA薄膜上，导致薄膜内部Au原位对Ag进行电化置换，形成Ag-Au粒子。通过电子显微镜和能量色散X射线光谱揭示了双金属纳米粒子向空心笼状结构的形态演变以及Au在纳米粒子上的分布。纳米复合薄膜的局域表面等离子体共振（LSPR）消光随Ag-Au组成而变化；消光谱的理论模拟为观察到的趋势提供了深入见解。发现Ag-Au-PVA薄膜是SERS的有效基底。EF随LSPR消光相对于激发激光波长的变化而变化，但有一个偏移，并且在非常低的Au含量下获得最大SERS效应；用罗丹明6G进行的实验表明EF约为10(8)，检测限为0.6 pmol。本研究描述了一种简便的纳米复合薄膜制备方法，该方法可方便地用于SERS研究，以及双金属系统在调节和最大化EF方面的实用性。
