Au-Graphene Oxide-Anodic Aluminum Oxide Nanostructured Substrates for Surface-Enhanced Raman Spectroscopy Based Molecular Sensing

We present surface-enhanced Raman scattering (SERS) enhancement studies in a biocompatible and chemically stable plasmonic composite based on gold nanoparticle decorated graphene oxides deposited over multiscale anodized aluminum oxide nanostructures. The underlying nanostructure in the fabricated sample increases the optical density of states in graphene oxides through maximum interaction volume for an electromagnetic wave from localized hotspots, which is important for the Raman signal enhancement. All samples are prepared through cost-effective two-step anodization techniques followed by wet-etching and drop-casting. It is observed that graphene oxide (GO)/Au and reduced graphene oxide (rGO)/Au composites have enhanced the absorption in these nanostructures to more than 90% due to strong localization of the electromagnetic field through the enhanced plasmonic effect. The surface morphologies of GO, GO/Au, rGO, rGO/Au, and composite nanostructures are done through Field emission-scanning electron microscope (FE-SEM) and ImageJ analysis. Raman characterization studies present signal enhancement up to 29-fold in the fabricated SERS substrate and fluorescence quenching of rhodamine 6G (R6G) molecules that may be applicable in molecular level/biomolecular sensing. Finite diference time domain (FDTD) simulation matches with the experimental study with an enhancement to the local field up to a factor of 3.3 x 10(3) at 532 nm, which is even more in higher wavelengths.