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 ─COOH groups. Under low‐intensity blue light (5 mW cm^{− 2}), Staphylococcus aureus is completely eliminated with just 0.8 µg mL⁻¹ of cGQDs, and a minimum bactericidal concentration (MBC) of 0.4 µg 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.