Ultra-Effective Light-Activated Antibacterial Activity via Carboxyl Functionalized Graphene Quantum Dots and Films

Abstract

Bacterial infections are a major healthcare concern. Clinical application of photo-activated quantum dots to efficiently treat bacterial infections has been hindered by inadequate production of reactive oxygen species. In this study, photoactive antimicrobial carboxyl-functionalized graphene quantum dots (cGQDs) are synthesized with an exceptionally high singlet oxygen (1O2) quantum yield of 0.88. Compared to non-functionalized GQDs, cGQDs exhibit over a 20-fold enhancement in the 1O2 quantum yield. According to the density functional theory simulations, the dramatic increase of 1O2 quantum yield is due to significantly enhanced spin-orbit coupling between singlet and triplet excited states of GQDs with addition of & horbar;COOH groups. Under low-intensity blue light (5 mW cm- 2), Staphylococcus aureus is completely eliminated with just 0.8 mu g mL-1 of cGQDs, and a minimum bactericidal concentration (MBC) of 0.4 mu g mL-1 is determined, representing the lowest MBC reported against S. aureus using light-activated quantum dots. Layer-by-layer assembly of cGQD films also results in over a 99.9% reduction against multi-drug resistant Staphylococcus aureus and Escherichia coli under illumination. cGQDs, both in suspension and as a nano-assembled film, exhibit good cell viability in mammalian cells under both dark and light conditions. These results highlight the strong potential of cGQDs as an effective nanomaterial for antibacterial applications.