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

Abstract

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.