Graphene Surface Improves SERS

A combined metal and graphene substrate improves the performance of surface-enhanced Raman spectroscopy (SERS), Jin Zhang of Peking University and coworkers report (Proc. Natl. Acad. Sci. USA, DOI: 10.1073/pnas.1205478109). Most SERS substrates have rough metal features that sometimes interact with analytes in a way that can complicate SERS spectra. Zhang and coworkers fabricate their new SERS substrate by depositing an array of gold or silver nanoislands on the back of a graphene monolayer. Like other SERS substrates, the metals have electromagnetic “hot spots” that enhance the Raman signal. In the new substrate, these hot spots permeate the graphene and generate localized electromagnetic enhancement on the flat surface. Analyte molecules bind on top of the flat surface, where they are isolated from the underlying metal. The researchers recorded SERS spectra of rhodamine 6G and copper phthalocyanine and found that those spectra are cleaner and more reproducible than spectra from conventional SERS substrates. The group demonstrated the method using a transparent, freestanding, and flexible form of the substrate, which allows direct analysis of samples of any morphology.