Tunable fluorescent biomass-derived carbon dots for efficient antibacterial action and bioimaging

Carbon dots (CDs)-based antibacterial biomaterials offer great potential in addressing the severe threat of antibiotic-resistant bacteria to public health. Positively charged CDs usually adhere on bacterial membranes via electrostatic interactions, however, they may cause hemolysis and cytotoxicity, and dissatisfactory fluorescence emission restricts their applications in bioimaging. Herein, we developed a negatively charged tunable multicolor nitrogen and phosphorus co-doped CDs (N, P-CDs) from mango peel, a renewable food waste biomass. The N, P-CDs exhibit good biocompatibility and photostability, thus could be adopted to multicolor cell labeling in vitro. More importantly, the negatively charged N, P-CDs possess intrinsic antibacterial activity against E. coli and S. aureus, and antimicrobial mechanisms were investigated by real-time quantitative PCR (RT-qPCR). We found the different mechanisms of N, P-CDs against E. coli and S. aureus, the antibacterial mechanism of N, P-CDs against E. coli mainly involve inhibition of binary fission proliferation and transcription of genetic information, interference with carbon metabolism and sugar conversion, thus inducing growth arrest and cell death. For S. aureus, N, P-CDs could serve as quorum sensing (QS) inhibitor to disrupt QS system, inhibit biofilm formation, DNA replication, cell division, and signal transmission. Our study provides important insights into antibacterial mechanism of CDs at the molecular level, which may facilitate the further exploration and application of natural resources-based antibacterial biomaterials.