Large-scale synthesis of gallic acid-derived carbon quantum dots as efficient photodynamic antimicrobial materials

Due to bacteria developing resistance to antibiotics, traditional antibacterial strategies face limitations. This study provides a microwave confined heating strategy for achieving gram-scale (yield: 10.8 g/batch) preparation of gallic acid-derived carbon dots (GA-CDs). Transmission electron microscopy results indicate that the GA-CDs possess a relatively small average particle size (2.92 ± 0.27 nm), which facilitates their penetration through the lipid bilayers of bacteria, thereby exhibiting superior antibacterial activity. The systematic analysis results indicate that the GA-CDs are primarily composed ofC, N, and O elements, featuring a highly carbonized graphite core, with some functional groups from the precursor retained on the core surface. Optical tests indicate that the GA- CDs have a maximum absorption wavelength at 457 nm and exhibit excellent photo-responsive reactive oxygen species performance. In addition, GA-CDs presents excellent photostability after continuous ultraviolet irradiation for 130 h. Excitation-independent tests indicate that the GA-CDs possess a stable energy level structure. Finally, experiments demonstrated that the minimum inhibitory concentration of the GA-CDs (16 μg mL^-1) is significantly lower than that of pure gallic acid (5 mg mL^-1), with a minimum bactericidal concentration of 50 μg mL^-1. This work provides a high-yield strategy for fabricating long-wavelength-absorbing, ultrasmall gallic acid derived CDs, offering a promising photodynamic approach to circumvent antibiotic resistance.