Sustainable EGCG:ε-Poly- l -lysine Polymer Dots: A Green Multifunctional Platform Integrating Potent Antibacterial Action and Cellular Imaging

ε-Poly- l -lysine (ε-PL) and epigallocatechin-3-gallate (EGCG) possess potent antibacterial properties; however, high aqueous solubility remains a major barrier to their use in stable surface coatings and solid-state systems. To overcome this limitation, we report a green and facile synthesis of novel, insoluble EGCG:ε-PL polymer dots via conjugation at varying stoichiometric ratios. The polymer dots were insoluble in common solvents, displayed excellent solid-state fluorescence, and high biocompatibility (98% inhibition of methicillin-resistant Staphylococcus aureus (MRSA) at 25 μg/mL. Consequently, the polymer dots were successfully applied as antimicrobial coatings on cotton gauze. Mechanistic studies revealed ROS-mediated antibacterial action and membrane disruption, supported by DCFH-DA assays, live/dead staining, and SEM analysis. Furthermore, the dots displayed antioxidant activity, and their intrinsic fluorescence enabled effective bacterial cell labeling and HeLa cell imaging with minimal mammalian cytotoxicity. Overall, EGCG:ε-PL polymer dots represent a sustainable, multifunctional platform for antibacterial coatings and biomedical applications.