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

## TL;DR

This paper describes a green method to create RGO/AuNPs nanocomposites with antimicrobial and cytotoxic properties for biomedical applications.

## Contribution

A one-step, eco-friendly synthesis method for RGO/AuNPs nanocomposites with demonstrated antimicrobial and cytotoxic effects.

## Key findings

- RGO/AuNPs nanocomposites showed strong antibacterial activity against E. coli, S. aureus, and B. subtilis.
- Higher RGO content increased cytotoxicity in HaCaT cells but maintained acceptable viability at low concentrations.
- The nanocomposites retained antimicrobial activity in protein-rich environments, indicating biomedical potential.

## Abstract

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 Escherichia coli, Staphylococcus aureus, and Bacillus subtilis, with sample RGO/Au 0.500/0.175 g/L showing complete E. coli 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.