Sustainable EGCG:ε-Poly- <scp>l</scp> -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 (<5% hemolysis at 200 μg/mL). Structural characterizations (SEM, FTIR, XPS, and XRD) confirmed successful formation of the polymer dots. Among the synthesized polymer dots, EGCG:ε-PL (1:2) demonstrated potent broad-spectrum antibacterial activity against Bacillus subtilis and Escherichia coli at 10 μg/mL. Notably, they exhibited strong efficacy against clinically isolated multidrug-resistant pathogens, achieving 100% inhibition of Pseudomonas aeruginosa at 10 μg/mL and >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.