One-pot synthesis of multicolor carbon quantum dots for broad-spectrum antibacterial applications

Multicolor carbon quantum dots (CQDs) emitting green (G-CQDs), yellow (Y-CQDs), and orange (O-CQDs) fluorescence were simultaneously synthesized via a one-pot solvothermal method. The CQDs exhibited excitation-independent photoluminescence with emission peaks at 496 nm (G-CQDs), 528 nm (Y-CQDs), and 561 nm (O-CQDs). Comprehensive structural and spectroscopic analyses confirmed their graphitic carbon frameworks, with graphitization levels increasing in parallel with emission wavelength from G-CQDs, Y-CQDs to O-CQDs, while quantum yields decreased inversely (43 %, 38.6 %, and 14.4 %, respectively), highlighting a trade-off between graphitization and fluorescence efficiency. The FTIR and XPS analyses show that these CQDs have distinct functional groups and atomic compositions, contributing to their diverse properties. Biocompatibility assays demonstrated low cytotoxicity and excellent hemocompatibility for all CQDs. For the antibacterial effects among the synthesized variants, Y-CQDs exhibited superior antibacterial activity against Enterohemorrhagic Escherichia coli (EHEC), Pseudomonas aeruginosa (P. aeruginosa), Klebsiella pneumoniae (K. pneumoniae), and Staphylococcus aureus (S. aureus), significantly outperforming conventional antibiotics. Mechanistic studies indicate that reactive oxygen species (ROS) generation, membrane disruption, and stress protein modulation are key mechanism for the antibacterial ability, which is particularly pronounced in Y-CQDs. These findings highlight Y-CQDs as promising candidates for antibacterial and biomedical applications.