Preparation and characterization of Ag-nanostars@Au-nanowires hierarchical nanostructures for highly sensitive surface enhanced Raman spectroscopy

In this work we study the surface enhanced Raman scattering (SERS) produced by hierarchical nanostructures obtained by coupling different anisotropic nanomaterial of two SERS active metals, namely Ag nanostars (AgNSs) and Au nanowires (AuNWs). Ag nanostars (AgNSs) are prepared, by a two-step one-pot synthesis by reduction of AgNO3 with hydroxylamine, trisodium citrate and NaOH. AuNWs are obtained by electroless templated synthesis in track-etched polycarbonate membranes with following etching of the template. The two precursors are bound together by bridging with the bifunctional cysteamine molecule, obtaining AgNS@AuNW hierarchical structures. Benzenethiol (BT) is adsorbed on the nanostructured material and used as SERS probe to study the amplification of Raman signals. Experimental results indicate significantly larger Raman enhancement when BT is adsorbed onto the AgNS@AuNW in comparison to AuNWs alone or decorated with quasi-spherical silver nanoparticles obtaining AgNP@AuNW. Digital simulations performed by the boundary element method agree with the experimental findings, showing higher number of hot spots and significantly higher SERS enhancements for AgNS@AuNW versus AuNWs or AgNSs or AgNP@AuNW.