Comparison of surface-enhanced Raman scattering on graphene oxide, reduced graphene oxide and graphene surfaces

To explore the role of the interaction between the adsorbed molecules and substrates for the charge transfer (CT) induced Raman enhancement, we systematically study the surface enhanced Raman scattering (SERS) on graphene, graphene oxide (GO) and reduced graphene oxide (r-GO) using rhodamine 6G (R6G) as the probe molecule. The Raman spectra of R6G molecules deposited on these three SERS substrates show remarkable difference in spectral features due to the different enhancement contributions from the local chemical groups and the global π-conjugation network of the substrates. What is more surprising is that for 1–4 layers graphene-based materials, the Raman signals of R6G on GO are found to increase intensity with the number of GO layers, while the Raman signals of R6G on different graphene/r-GO layers show inverse trends due to dominant π–π stacking mechanism. Our results provide a comprehensive understanding of the influence of local chemical groups and the global π-conjugation network on the SERS enhancements. In addition to high reproducibility, low cost, and good biocompatibility of GO, the rich chemical structures and the absence of electromagnetic enhancement make it an excellent choice as a tunable substrate to study the chemical enhancement resulting from the adsorbent–substrate interaction.