Shikonin-copper coordination nanoparticles for enhanced antibacterial and antibiofilm activity against Staphylococcus aureus

Antimicrobial resistance (AMR) poses a critical global health challenge, with an estimated 1.27 million AMR-attributable deaths in 2019 and projections of 39 million cumulative deaths from 2025 to 2050, particularly driven by Staphylococcus aureus and methicillin-resistant strains (MRSA) that form robust biofilms conferring up to 1000-fold antibiotic tolerance and complicating hospital-acquired infections. Here, we report a green, one-pot synthesis of shikonin-copper nanoparticles (SCu NPs), employing shikonin (SK)-a naphthoquinone from Lithospermum erythrorhizon roots-as a dual chelator and stabilizer, without exogenous reductants or surfactants; density functional theory (DFT) computations guide the design, predicting thermodynamically favored 1:2 Cu(II): SK stoichiometry, yielding stable spherical nanoparticles (39.25 ± 3.24 nm) with preserved Cu(II) oxidation state, as validated by TEM, XPS, XRD, and UV-Vis spectroscopy. SCu NPs exhibit potent antibacterial activity against S. aureus ATCC 25,923, with minimum inhibitory and bactericidal concentrations (MIC/MBC) of 4/8 µg/mL-half those of SK (8/16 µg/mL)-and rapid bactericidal kinetics, reducing viability by 66% within 2 h; antibiofilm assays reveal concentration-dependent inhibition, achieving up to 89% biomass reduction at 32 µg/mL, outperforming SK, CuSO₄, and their mixture, with SEM confirming extensive membrane disruption and cytoplasmic leakage. This synergy arises from Cu(II)-mediated reactive oxygen species (ROS) generation, enhanced lipophilicity, and SK's quorum-sensing inhibition, positioning SCu NPs as a sustainable, multi-target platform integrating natural product chemistry and nanotechnology to combat biofilm-associated AMR, mitigate resistance emergence, and advance therapeutics for recalcitrant infections.