Engineering Synergistic and Stable Polycatechin-Capped Copper Nanoparticles as a Green Nano-Antibacterial Platform Against Resistant Pathogens and Biofilms

Background: Copper nanoparticles (CuNPs) are promising antibacterial agents, but instability and heterogeneity in ‘green’ routes limit translation. Methods: We developed a one-step synthesis in which pre-polymerized polycatechin acts as both reductant and capping agent to form copper–polycatechin core–shell nanoparticles (Cu@polycat). Physicochemical properties (TEM/DLS/XRD/FTIR/ζ), colloidal stability (pH, salt, serum), ion release, and antibacterial activity against planktonic and biofilm E. coli/S. aureus were evaluated. Results: Cu@polycat featured a ~21.5 nm metallic core and ~45 nm hydrodynamic diameter (shell ≈ 12 nm, estimated from TEM–DLS) with ζ ≈ −34 mV, conferring high stability across physiological conditions. Cu@polycat outperformed uncoated CuNPs, displaying 8-fold lower MICs and rapid bactericidal kinetics (>5-log10 in 6–8 h). Synergy between the copper core and polycatechin corona was confirmed (FICI ≈ 0.08). Cu@polycat inhibited biofilm formation by >80% and reduced viable counts in 24 h mature biofilms by ≥3-log10, whereas ampicillin was ineffective under the same biofilm conditions. Conclusions: A polycatechin-based green route furnishes a stable, synergistic nano-antibacterial platform with potent anti-biofilm activity, supporting development for wound-care and anti-fouling device coatings.