Antibacterial carbon dots integrating multiple mechanisms for selective Gram-positive bacteria elimination and infected wound healing acceleration.

The escalating prevalence of multidrug-resistant Gram-positive bacterial infections demands the development of antimicrobial agents with precise targeting and rapid bactericidal activity. In this study, ultra-small positively-charged carbon dots (PR-CDs) were synthesized through a one-step hydrothermal synthesis of polyethyleneimine and Rhodamine B. The resulting PR-CDs exhibited multiple antibacterial mechanisms: (1) electrostatic attraction to Gram-positive bacterial membranes, (2) cellular internalization enabled by their ultra-small size (2.3 nm), and (3) visible light-activated reactive oxygen species (ROS) generation. PR-CDs have shown selective bactericidal activity against methicillin-resistant (MRSA) and other Gram-positive pathogens with minimum bactericidal concentrations as low as 19.53 μg mL under light irradiation. Mechanistic studies revealed that the positive charges on the surface of PR-CDs facilitated selective binding to teichoic acid-rich Gram-positive cell walls, while their nanoscale dimensions permitted deep penetration into bacterial cells, enhancing oxidative damage through rapid generation of singlet oxygen (O). Encapsulation of PR-CDs in gellan gum (PR-CDs@GG) hydrogels enabled sustained ROS release and accelerated MRSA-infected wound healing in MRSA-infected mice, achieving 82.51% wound closure within 8 days without systemic toxicity. This work establishes a paradigm for precision antimicrobial design integrating targeted binding, cellular penetration, and photodynamic activation.