Carbon Quantum Dots as Emerging Antibacterial Nanomaterials: Strategies to Enhance Their Activity

Carbon quantum dots (CQDs) exhibit multiple antibacterial mechanisms, making them more effective than conventional antibiotics, which typically act through a single mode of action. These mechanisms include membrane disruption, biofilm inhibition, reactive oxygen species (ROS) generation, and photodynamic (PDT) or photothermal (PTT) effects under light irradiation. Extensive research has been conducted to reinforce these mechanisms and improve the antibacterial performance of CQDs, aiming to reduce required CQD dosages and combat bacterial resistance. This review systematically summarizes structural and functional design strategies reported since 2020. We categorized these strategies into selecting antibacterial molecules as precursors, controlling particle size, surface modification, doping with non-metal and metal elements, and forming functional composites to enable light activation, synergetic effects, and multifunctionality. For each category, we provide representative CQD examples, in terms of their preparation, physicochemical properties contributing to antibacterial performance, and possible structure–activity relationships. Finally, the review highlights limitations and proposes future research directions for developing antibacterial CQDs for clinical translation.