Structural Characterization, Cytotoxicity and Microbiological Activity of One-Step-Synthesized RGO/AuNPs Nanocomposites

This study presents a green, single-step method for synthesizing nanocomposites based on reduced graphene oxide (RGO) and gold nanoparticles (AuNPs), using sodium citrate as a mild reducing and stabilizing agent. AuNPs were generated from chloroauric acid (HAuCl₄) directly on the surface of graphene oxide (GO), which was simultaneously reduced to RGO. Structural characterization via Transmission Electron Microscopy (TEM), High Resolution TEM (HRTEM) and Selected Area Electron Diffraction (SAED) confirms spherical AuNPs (10-60 nm) distributed on RGO sheets, with indications of nanoparticle aggregation. Dynamic Light Scattering (DLS) and zeta potential analysis support these findings, suggesting colloidal instability with higher RGO content. Biological evaluation demonstrates dose-dependent cytotoxicity in HaCaT keratinocytes, with IC₅₀ values (half maximal inhibitory concentration) decreasing as RGO content is increased. At moderate dilutions (1-25 µL/100 µL), the composites show acceptable cell viability (>70%). Antibacterial assays reveal strong synergistic effects against <i>Escherichia coli</i>, <i>Staphylococcus aureus</i>, and <i>Bacillus subtilis</i>, with sample RGO/Au 0.500/0.175 g/L showing complete <i>E. coli</i> inhibition at low Au content (0.175 g/L). The composite retained activity even in protein-rich media, suggesting potential for antimicrobial applications. These findings highlight the potential of RGO/AuNPs composites as multifunctional materials for biomedical uses, particularly in antimicrobial coatings and targeted therapeutic strategies.