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 significant interest. However, the concern about the necessity of removing oxygen containing functional groups in graphene oxide (GO) modification for biomedical applications has not been extensively studied. Here, we synthesized graphene oxide (GO) and reduced graphene oxide (rGO) modified 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 effective at inhibiting E. coli growth (52% growth inhibition), while rGO-Au was significantly 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 findings 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 specific bacteria like S. aureus. This suggests that preserving the oxygen-containing functional groups in other GO modifications is preferable in the biomedical field to maintain the low toxicity of graphene-based materials and their bioavailability.