基于自组装纳米金单层膜的全内反射SERS研究

采用静电自组装技术分别在玻璃基片和30 nm厚的金膜表面固定一层金纳米粒子(GNP)制得两种表面增强拉曼散射(SERS)基底,然后通过棱镜全内反射(TIR)激励和背向收集模式分别测试了两种基底上吸附的染料单分子层SERS光谱.实验结果表明两种SERS基底的拉曼增强效果均高度依赖于入射激光的偏振状态,对于玻璃/纳米金SERS基底,s光全内反射导致的拉曼增强因子是线偏振光(p)光的2-5倍,说明该基底上的"热点"位于纳米金单层膜内相邻粒子之间;对于玻璃/金膜/纳米金SERS基底,只有采用p光在特定的全内反射角下才能激发SERS信号,而且测得的SERS信号比玻璃/纳米金基底增强了近30倍.究其原因是p光在金膜表面共振激发的传播表面等离子体与纳米金局域表面等离子体耦合,进而导致显著场增强.实验结果指出在背向收集模式下,由p光激发的SERS信号是非偏振光,包含强度几乎相等的s和p成分.利用玻璃/金膜/纳米金基底还实现了拉曼光定向发射和收集,测得的SERS信号是p光.

Study of Total Internal Reflection SERS Based on Self-Assembled Gold Nanoparticle Monolayer Film

Two types of Surface Enhanced Raman Scattering (SERS) substrates were prepared by selfassembly of gold nanoparticle (GNP) monolayers film on either bare glass substrates (glass/GNP) or glass substrates with a 30 nm thick gold film (glass/Au/GNP). SERS spectra of dye molecules adsorbed on the two substrates were obtained by total internal reflection (TIR) of an excitation laser beam combined with collection of the air-side signal. The experimental results demonstrated that the signal enhancement factors of the two SERS substrates greatly depend on the polarization state of the excitation beam. In the case of the glass/GNP substrate, the signal enhancement factor obtained with the s-polarization TIR is two to five times as higher as that observed with the p-polarization TIR, indicating the formation of“hot spots”between adjacent particles in the GNP monolayer. With the glass/Au/GNP substrate, the SERS signal can be excited only by p-polarization TIR at a specific reflection angle, and the air-side SERS signal is almost 30 times that obtained with the glass/GNP substrate. The findings suggest that significant field enhancement is induced by the coupling between propagating surface plasmon resonance (SPR) and the localized SPR within the glass/Au/GNP substrate. Using a linear polarizer, the air-side SERS signal was verified to be non-polarized, containing s and p components of almost equal intensities. Further investigations revealed that the glass/Au/GNP substrate allows for directional emission of the SERS signal with the p-polarization state.