SERS response from gap-enhanced Raman tags as a function of the shell thickness

Abstract

Tags based on surface-enhanced Raman scattering spectroscopy (SERS tags) contains a plasmon-resonant core and Raman reporter molecules located in the area of high local electromagnetic field. These tags are widely used in bioimaging and sensing. Gap enhanced Raman tag (GERT) is a novel type of SERS tag which consists of a plasmon core coated by noble metal shell with Raman reporter molecules embedded between metal layers. The optical properties of these particles are determined by the material and size of the core and shell, the thickness of the internal gap containing reporter molecules, and also by the laser wavelength. From the point of view of its optical and chemical properties, gold is one of the most suitable materials for the synthesis of the core and shell. However, it is necessary to select the optimal parameters for the synthesis of GERTs with the maximum enhancement of the SERS signal. In this work we examined the dependence of SERS signal of gold nanorod-based GERTs from the thickness of outer gold shell by using a Raman spectrometer with a wavelength of 785 nm, which is inside the transparency window of biological tissues. It is known that the intensity of SERS signal from the Raman reporter molecules incorporated inside the intermetallic gap is highly dependent from the gold shell thickness. We found that with a decrease in the gold shell thickness from 51 nm a gradual decrease in the intensity of the SERS signal is observed.