Straightforward microwave-assisted synthesis of ultrasmall gold nanoparticles acnhored on reduced graphene oxide for enhanced antibacterial application

Graphene derivative materials, such as graphene oxide (GO) and reduced graphene oxide (rGO), have garnered signifcant
attention from scientists for over two decades due to their distinctive characteristics and versatile applications across
various felds, particularly in biomedical applications. Incorporating gold nanoparticles (AuNPs) into rGO sheets as rGO-Au
nanocomposites further enhances its performance in biomedical applications. This study presents a rapid and efcient
method for synthesizing ultrasmall AuNPs anchored on reduced graphene oxide (rGO-Au) using microwave irradiation
and ascorbic acid. The optimum microwave treatment was 4 min, ensuring the highest GO reduction degree. Structural
characterization by TEM reveals a distinctive architecture with ultrasmall AuNPs (average size of 2.2 nm) distributed
on the rGO sheets. Interestingly, while the synthesized rGO-Au did not exhibit any antibacterial activities against both
Escherichia coli and Staphylococcus aureus in disk difusion assays, it demonstrated bacteriostatic efect at remarkably
low concentrations when assessed by optical density measurement. The efective concentration of rGO-Au to inhibit E.
coli growth was determined to be 2.5 ppm, while for S. aureus, it was 5 ppm, resulting in growth inhibition of 53.1% and
50.0%, respectively. These fndings provide a straightforward synthesis route for rGO-Au nanocomposites and underscore
the importance of AuNPs’ size and quantity in modulating antibacterial properties.