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 I
D/I
G,
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 × 104,
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.
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