Strained alkyne functionalization of carbon dots enables selective photodynamic killing of Gram-positive bacteria.

Metal-free photoactive nanomaterials offer a promising strategy to address antimicrobial resistance, yet strategies enabling tuneable and efficient activity remain limited. Here, we introduce a materials-led approach to antibacterial photodynamic therapy by engineering carbon dots (CDs) with a strained dibenzocyclooctyne (DBCO) surface motif. Direct installation of the strained alkyne yields photoresponsive DBCO-CDs that exhibit potent, selective light-activated antibacterial activity. Under low-energy LED irradiation (395-405 nm), DBCO-CDs achieve >99.9% inactivation of Gram-positive bacteria, including Staphylococcus aureus, while remaining inactive in the dark and against Gram-negative bacteria. Mechanistic studies reveal that the intact strained alkyne is essential for activity, with non-strained-featuring analogues showing no efficacy. Reactive oxygen species (ROS)-trapping experiments implicate H2O2-mediated oxidative stress, while sub-cellular fluctuation imaging demonstrates rapid collapse of intracellular dynamics, consistent with metabolic failure. Notably, DBCO-CDs disrupt established biofilms, reducing biomass by 57% upon irradiation. Collectively, our findings establish strained-alkyne surface engineering as a powerful and modular strategy for imparting photodynamic functionality to carbon nanomaterials, advancing next-generation antimicrobial and antibiofilm technologies.