Synergistic antibacterial activity of PEGylated silver–graphene quantum dots nanocomposites

Abstract

The emergence of antibiotic-resistant bacteria is a major threat to world-wide public health. Functionalized nanoparticles could offer novel strategies in this post-antibiotic era. In this study, we developed nanocomposites of silver nanoparticles decorated with graphene quantum dots (Ag-GQDs) using pulsed laser synthesis. The nanocomposites were PEGylated, which increases their biocompatibility and solubility in aqueous solutions. The HR-TEM micrographs of bare GQDs show that their size is in the range of 1.6–4nm, and the lattice spacing is 0.214nm, which corresponds to the (100) lattice fringes of graphene. The antibacterial activity of Ag-GQDs was evaluated and compared to that of bare GQDs and commercial silver nanoparticles (Ag-NPs) against both Gram-negative and Gram-positive bacteria, using Pseudomonas aeruginosa and Staphylococcus aureus as model bacteria, respectively. Concentration values of 25 and 50μg/mL are required for Ag-GQDs to inhibit the growth of S. aureus and P. aeruginosa bacteria, respectively. The fractional inhibitory concentration (FIC) index is below 0.5 indicating that there is a synergistic effect between Ag-NPs and GQDs. Kirby–Bauer tests showed that Ag-GQDs inhibit P. aeruginosa and S. aureus, in contrast to bare GQDs and Ag-NPs alone. Cell viability of normal mammalian cells treated with Ag-GQDs showed that cell viability is maintained at 100% for cells incubated with Ag-GQDs. The decoration of Ag-NPs with GQDs minimizes their cytotoxicity in mammalian cells and increases their biocompatibility. Ag-GQDs have potential applications in the fabrication of antibacterial coatings, self-sterile textiles, and personal care products.