Novel graphene oxide/nano-gold platforms for optimized SERS detection

Surface-enhanced Raman scattering (SERS) spectroscopy has emerged as a powerful ultrasensitive analytical technique in biosensing. The SERS effect relies on huge electromagnetic fields concentrated at the nanostructured metal surface to dramatically enhance the Raman signal of molecules when localized surface plasmon resonances (LSPRs) are excited by an external incident electromagnetic wave. Efficient SERS enhancements are typically generated within less than 10 nm from the metal surface and are mostly confined within the so-called "hot spots", i.e. highly curved nanoregions or gaps and junctions between adjacent nanoparticles. The ability to gather molecules in these regions in a homogeneous and reproducible manner represents a current impediment that is still preventing further diffusion of SERS as a systematic analytical tool. Here we present the use of nonspherical tipped metallic nanostructures with controlled architectural parameters and their assembly into organized bidimensional arrays including a regular distribution of hot spots for protein entrapment and detection [1]. The investigation evidenced that both the contact points between nanoparticle corners and the holes at the interface between nanoparticles are responsible for substantial SERS activity. A further advancement toward upgrading the performance of SERS technology relies on the combination of plasmonic nanostructures with graphene oxide. Current efforts are taking advantage of a thin graphene oxide coating in drawing and concentrating target molecules as well as in conferring the plasmonic surface with a passivating layer that discards possible disturbances and signal variability induced by metal- molecule interactions. We present an effective graphene oxide/plasmonic substrate with a highly controlled and uniform bilayer structure. The substrate was obtained by fine-tuning in silver nanocubes self-assembly, followed by a controlled adsorption of graphene oxide sheets on the silver layer. Here the graphene oxide coating supplies the signal with additional amplification. The developed system shows a highly uniform signal distribution ascribed to a homogeneous and soft arrangement of graphene oxide sheets over the plasmonic surface, which makes it a reliable tool for detecting different compounds ranging from small molecules to complex biomolecules [2]. [1] P. Matteini, M. de Angelis, L. Ulivi, S. Centi, R. Pini, Concave gold nanocube assemblies as nanotraps for surface-enhanced Raman scattering-based detection of proteins, Nanoscale, vol. 8, 3374-3480, (2015). [2] M. Banchelli, B. Tiribilli, M. de Angelis, R. Pini, G. Caminati, P. Matteini, Controlled veiling of silver nanocubes with graphene oxide for improved Surface enhanced Raman scattering detection, ACS Applied Materials & Interfaces, vol. 8, 2628-2634, (2016).