Carbon dots derived from folic acid as an ultra-succinct smart antimicrobial nanosystem for selective killing of S. aureus and biofilm eradication

Developing efficient and safe approach to counteract the bacterial infections has become an urgent clinical challenge. In this work, we report folic acid derived carbon dots (FA-CDs) prepared by a one-step pyrolysis method. The FA-CDs can respond to the environmental stimuli of bacterial infections and acquire antimicrobial capacity "on demand" as a simple and effective antimicrobial nanosystem. The assays on antibacterial properties and mechanism show that FA-CDs are able to induce the gradual increase of intracellular reactive oxygen species (ROS) levels in bacteria under the simulated acidic environment and display pH-responsive biocidal activity. In a neutral condition, FA-CDs have no antibacterial activity, which will be conducive to mitigating the rise of bacterial drug resistance. The responsive antibacterial behavior can be attributed to that FA-CDs exhibit distinctive oxidase-like and peroxidase-like activity under acidic stimuli and inhibit the superoxide dismutase activity in bacteria cells, causing the accumulation of intracellular ROS. Meanwhile, FA-CDs can selectively kill Gram-positive bacterium S. aureus and remove mature biofilms. Besides, the in vitro and in vivo experiments demonstrate that FA-CDs possess excellent biocompatibility, and show remarkable therapeutic effect on the S. aureus-infected back wound models of mouse, which are crucial for clinical applications. Thus, this study highlights the potential application of FA-CDs as an ultra-succinct smart antimicrobial nanosystem for coping with infections caused by S. aureus in the clinical setting, and will bring about a new perspective on developing antimicrobial CDs.