Plasma-Treated Graphene Surfaces for Trace Dye Detection Using Surface-Enhanced Raman Spectroscopy

Trace detection using reliable, highly stable, cost-effective, and high-performing substrate materials remains a challenging problem. In the present report, extra-large-size graphene oxide (GO) sheets are exfoliated using a simple mild heating technique and subsequently reduced to remove the attached oxygen functional groups by thermal treatment without losing their size for the sensing application using surface-enhanced Raman spectroscopy. The microscopic structure of the GO is studied by using the optical microscope, field emission scanning electron microscope, atomic force microscope, and field emission transmission electron microscope imaging. The nature of GO and reduced GO (RGO) is confirmed from the X-ray diffraction, Raman, X-ray photoelectron spectroscopy, and Fourier transform infrared (FTIR) analyses. The structure of GO and RGO is modified using gas plasma treatment, which is evidenced from the Raman analysis showing a shift in peak positions, change in full width at half maximum of peaks, D'-G, and ID/IG, and substantiated by FTIR analysis. The surface-enhanced Raman spectroscopy (SERS) effect of the dye Rhodamine B (RhB) on GO/RGO is selectively more enhanced as compared to the methyl orange (MO), methyl blue (MB), and rose Bengal dyes. We show that Ar plasma treatment of GO yields the highest enhancement factor (EF) of 1.3 x 10(4), which is one of the highest among the reported values. Using the large area GO, we demonstrate a detection limit of the 10(-8) M RhB dye. To isolate the contributions of the functional groups and defects in the observed EF, we performed vacuum annealing of the large-area GO and elucidated the role of defects in the high EF observed in the Ar plasma-treated GO. Hence, the large-area GO with an appropriate plasma treatment could be a potential avenue for use as a SERS substrate for application in trace detections.