Multifunctional carbon quantum dots: green synthesis, bright emission, and pathogen suppression

Nitrogen and sulfur co-doped carbon quantum dots (N, S-CQDs) have emerged as promising nanomaterials due to their excellent photoluminescent properties and potential biomedical applications, particularly in combating antimicrobial resistance and biofilm-associated infections. This study presents the green solvothermal synthesis and detailed characterization of N, S-CQDs using citric acid and N-acetyl-L-cysteine as precursors. Physicochemical analysis revealed strong fluorescence, abundant surface functional groups, almost neutral zeta potential, and good structural stability. Antimicrobial testing showed that the synthesized CQDs exhibited significant activity against various bacterial pathogens (MICs: 4.375–17.5 mg/mL) and Candida albicans (MIC: 35 mg/mL). They also showed strong antibiofilm properties, eliminating mature biofilms by up to 74 % and decreasing biofilm production by 75 % to 85 %. Interestingly, the CQDs retained their optical integrity upon microbial contact, with the emission peak remaining stable across tested microorganisms. The effectiveness of N, S-CQDs as antimicrobial and antibiofilm agents is supported by these findings.