Assembly of graphene oxide and Au _0.7Ag _0.3 alloy nanoparticles on SiO ₂: A new Raman substrate with ultrahigh signal-to-background ratio

Resonance Raman spectroscopy (RRS) often suffers from the large fluorescence background which obscures the much weaker Raman scattering. To address this fundamental problem, a novel Raman substrate has been fabricated by adsorption of Au _0.7Ag _0.3 alloy nanoparticles (NPs) on a graphene oxide (GO) coated SiO ₂ surface, which offers both excellent Raman enhancement and fluorescence quenching. Our experimental data reveal that a Raman to fluorescence background intensity ratio of 1.6 can be obtained for a highly fluorescent dye like Alexa fluor 488. Moreover, we demonstrate that the Raman enhancement mainly originates from the Au _0.7Ag _0.3 alloy NPs and that the fluorescence quenching mainly arises from the underlying functionalized GO (FGO) substrate.