Bimetallic gold core–silver shell nanorod performance for surface enhanced Raman spectroscopy

Abstract

Plasmonic gold nanorods (AuNRs) coated with four different thickness silver shells (AuNR\Ags) were synthesized and tested for their efficiency in Surface Enhanced Raman Scattering (SERS) signal enhancement for biomedical applications. Both AuNRs and AuNR\Ags were prepared using a modified seed-mediated method and then characterized using TEM, XPS and UV-vis spectroscopy. All four bimetallic nanorods used in our experiments started from gold nanorod (AuNR) cores (of 36 nm length and 12 nm diameter) which were coated with a 0, 1, 2, 3 or 4 nm thick layer of silver. SERS spectra were obtained for each thickness of AuNR\Ag Raman agent using a Raman reporter – organic molecule p-aminothiophenol (PATP). Moreover, to confirm experimental findings a numerical model was built using COMSOL Multiphysics and solved for a single AuNR\Ag interaction with light on a silica substrate. The highest SERS signal at the incident wavelength of 784 nm, was observed for AuNR\Ags coated with a 1 nm thick silver shell. The numerical model confirmed experimental findings and predicted the highest near-field enhancement in the vicinity of nanoparticles on top of a silica substrate at 784 nm wavelength, for an AuNR\Ag with the same 1 nm silver shell thickness.