Improved Sensitivity of Surface-Enhanced Raman Scattering with Gold Nanoparticles-Insulator-Metal Sandwich Layers on Flat Sapphire Substrate.

Wenbing Li,Zhuo Yang,Bo Liu,Xin Tong,Jiali Zhang,Chao Ping Chen

doi:10.3390/nano11092416

Abstract

Surface-enhanced Raman scattering (SERS) as a high sensitivity analytical method for molecule detection has attracted much attention in recent research. In this work, we demonstrated an improved SERS substrate, which has the gold nanoparticles randomly distributed on a SiO2 interception layer over a gold thin film layer on the flat sapphire substrate (AuNP/SiO2/Au/Sapphire), over the dispersed gold nanoparticles on a silicon substrate (AuNP/Si), for detection of R6G (1 × 10−6 M) in a Raman microscope. The fabrication of sandwich layers on top of the sapphire substrate involves evaporation of a gold mirror as thick as 100 nm, plasma enhanced chemical vapor deposition of the silica insulator layer 10 nm thick, and evaporation of a thin gold layer 10 nm thick for forming gold nanoparticles. For comparison, a gold thin film with a thickness of 5 nm and 10 nm was evaporated on a silicon substrate, respectively (AuNP/Si), as the reference SERS substrates in the experiment. The AuNP/SiO2/Au/Sapphire substrate demonstrated improved sensitivity in detection of molecules in Raman microscopy, which can enable the molecules to be recognizable at a low laser power as 8.5 × 10−3 mW, 0.017 mW, 0.085 mW, and 0.17 mW for ultrashort exposure time. The simulation of AuNP/SiO2/Au/Sapphire substrate and AuNP/Si substrate, based on the finite-difference time-domain (FDTD) method, explained the improved sensitivity for detection of R6G molecules from the view of classical electromagnetics, and it suggested the optimized size for the gold nanoparticles and the optimized laser wavelength for Raman microscopy for further research.

Highlights

Surface-enhanced Raman scattering (SERS) has attracted interest for its high sensitivity in detection of molecules [1,2,3] since its discovery in 1974, in the testing of pyridine adsorbed on the surface of a silver electrode [4,5]
The three types of substrates, gold nanoparticles formed by 5 nm gold thin film on silicon substrate (AuNP/Si), gold nanoparticles formed by 10 nm gold thin film on silicon substrate (AuNP/Si), and AuNP/SiO2 /Au/Sapphire substrate were symbolized as sample S1, sample S2, and sample S3, respectively, after their preparation
We demonstrated that the gold nanoparticles-insulator-metal sandwich layers structure on the sapphire substrate had the advantage over the gold nanoparticles on the surface of silicon substrate for high sensitivity detection of R6G molecules in Raman microscopy, experimentally

Summary

Introduction

Surface-enhanced Raman scattering (SERS) has attracted interest for its high sensitivity in detection of molecules [1,2,3] since its discovery in 1974, in the testing of pyridine adsorbed on the surface of a silver electrode [4,5]. Since there are highly localized electric fields, namely, the “hotspots”. The molecules adsorbed on the high density “hotspots” contribute most of the enhancement for the surface enhanced Raman microscopy [22,24]. The chemical synthesized gold or silver colloids that are used as the substrate for enhancing the Raman scattering for detection of dyes started at least as early as the 1980s [13]. The production of the gold and silver colloids involves the use of hazard aqueous chemicals, such

Methods

Results

Conclusion