Study on SERS activity of Au-Ag bimetallic nanostructures synthesized using different reducing agents

Abstract

Abstract The Au-Ag bimetallic nanostructures were synthesized independently using three different reducing agents [ascorbic acid (C6H8O6), sodium borohydride (NaBH4) and tri-sodium citrate dihydrate (C6H9Na3O9)] to understand their effect on the morphology of the nanostructures. The nanostructures obtained using the reducing agents mentioned in above order, were found in sprouted potato, cubical, and prolate spheroid (PS) shapes. All the synthesized nanostructures were characterized using energy-dispersive X-ray spectroscopy and extinction spectroscopy. The surface enhanced Raman scattering (SERS) activity of all these nanostructures was studied using Raman probe solutions with micro and nanomolar concentrations. Relatively, the PS shaped nanostructures were found to be more stable and better for SERS studies. Therefore, these nanostructures were further characterized by Transmission electron microscopy and X-ray photoelectron spectroscopy. The usefulness of PS shaped Au-Ag nanostructures was also demonstrated by recording the spectra of both methylene blue (MB) and 4-Aminothiophenol (4-ATP) solutions with femtomolar concentration. The experimental enhancement factor (EEF) was found to be around 1.1 × 1011 in case of MB solution with femtomolar concentration. The possible origin for the EEF is explained using quasi-static theory and Finite Element Method (FEM) based simulations.