Lignin-based carbon dots with adjustable singlet oxygen production for antibacterial application

Bacterial resistance arising from antibiotic misuse necessitates the development of effective non-antibiotic antimicrobial agents. Herein, we report the synthesis of nitrogen-doped lignin-based carbon quantum dots (N,L-CQDs) with precisely adjustable singlet oxygen ( 1 O 2 ) production efficiency for photodynamic antibacterial therapy. A one-pot hydrothermal method using alkali lignin and ethylenediamine was employed to fabricate a series of N,L-CQDs (N,L-CQDs 1–4 ) with controlled nitrogen-doping levels. Comprehensive characterization reveals that nitrogen-doping enhances graphitization, modifies surface states, and creates in-gap emission centers, leading to tunable optical properties. Crucially, the 1 O 2 quantum yield (QY) was found to be directly dependent on the doping degree, with an optimal value of 82.61%, ranking the top among the reported for carbon-based photosensitizers. Theoretical calculations attribute the maximal 1 O 2 QY to a minimized singlet-triplet energy gap (Δ E ST  = 0.27 eV), which facilitates intersystem crossing (ISC). The optimized N,L-CQDs 3 demonstrate potent, light-activated bactericidal activity against both Escherichia coli ( E. coli ) and Staphylococcus aureus ( S. aureus ) via 1 O 2 -mediated oxidative damage. Furthermore, when incorporated into a hydrogel patch, N,L-CQDs 3 significantly accelerated the healing of infected full-thickness wounds in a murine model by eliminating bacteria, modulating inflammatory cytokines, and promoting collagen deposition. This study not only establishes a strategy for tuning the photodynamic efficacy of biomass-derived carbon dots but also underscores their significant potential as low-cost and efficient antibacterial agents for translational wound care.