Multimetallic Nanoparticles on Mirrors for SERS Detection

Nanoparticle on mirror (NPoM) architectures are attractive for optical applications-particularly for sensing-due to their simplicity and reliability of their multicomponent plasmonic interactions. However, to date, work has predominantly focused on monometallic nanoparticles on different metallic films. While these studies have investigated the effect of geometry on the optical responses of NPoM structures, understanding the effect of nanoparticle composition is needed to gain a full understanding and complete control over these systems. To elucidate the role of composition on localized plasmonic resonances, a surface-based nanoparticle synthetic method, scanning block copolymer lithography (SPBCL), was used to synthesize and characterize single Au0.5Ag0.5 particles on a five-layer, thermally stable plasmonic mirror substrate. The use of SPBCL is important because it can easily be extended to almost a limitless number of polyelemental systems. We demonstrate the potential of the approach by using surface-enhanced Raman spectroscopy to detect benzene-1,4-dithiol adsorbed onto individual alloyed AuAg NPs in an NPoM geometry.