A Comparative Study of the Effect of Oxygen-Containing Functional Groups in GO and rGO Sheets Decorated with Small Gold Nanoparticles on Bioactivities

The utilization of carbon-based materials in biomedicine, especially graphene derivatives, has garnered signifcant interest.
However, the concern about the necessity of removing oxygen containing functional groups in graphene oxide (GO) modifcation for biomedical applications has not been extensively studied. Here, we synthesized graphene oxide (GO) and reduced
graphene oxide (rGO) modifed with small gold nanoparticles (AuNPs) below 10 nm, referred to as GO-Au and rGO-Au,
respectively, and subsequently their antioxidant capability, antibacterial activity, and cytotoxicity were directly compared.
The rapid microwave-assisted synthesis method was employed to produce GO-Au and rGO-Au nanocomposites. Structural
and compositional analyses using various characterization techniques revealed distinctive properties between GO-Au and
rGO-Au. Interestingly, antioxidant assays employing DPPH and ABTS methods demonstrated that GO-Au exhibited higher
antioxidant activity than rGO-Au with IC50 values of 98.5 and 202.8 μg/mL, respectively. Antibacterial assays showed that
GO-Au was more efective at inhibiting E. coli growth (52% growth inhibition), while rGO-Au was signifcantly better
against S. aureus (99% growth inhibition) due to the distinct mechanisms of action. On the other hand, cytotoxicity assays
performed on Vero cells revealed that GO-Au exhibited greater biocompatibility compared to rGO-Au with IC50 values of
31.3 μg/mL and 23.4 μg/mL, respectively. These fndings emphasize the crucial role of oxygen-containing functional groups
in GO-based materials, particularly in GO-Au nanocomposites, for enhanced biocompatibility and bioactivity. Removing
oxygen groups, as seen in rGO-Au, is unnecessary, unless in cases targeting specifc bacteria like S. aureus. This suggests
that preserving the oxygen-containing functional groups in other GO modifcations is preferable in the biomedical feld to
maintain the low toxicity of graphene-based materials and their bioavailability.