Sustainable synthesis of bimetallic Cu–Ag nanoparticles using waste-derived chitosan and citrus extract: a green approach to combat antimicrobial resistance

Abstract

The growing threat of antimicrobial resistance necessitates innovative strategies that combine efficacy with environmental sustainability. Current methods for synthesizing bimetallic copper-silver nanoparticles often rely on hazardous chemicals or costly reagents, limiting sustainable production. This study presents a dual waste valorization approach to synthesize bimetallic Cu-Ag nanoparticles using Citrus sinensis peel extract as a reducing agent and chitosan from Archachatina marginata shells as a stabilizer in a single-pot aqueous process. Mild conditions (60 °C, atmospheric pressure, 4 h) avoided toxic solvents while transforming two abundant regional waste streams into functional nanomaterials. Chemical characterization confirmed the extract's reducing capacity: total phenolic content (1.759 mg GAE/g), total flavonoid content (0.298 mg QE/g), and antioxidant activity (DPPH: 62.61%; FRAP: 0.965 AU; HPS: 73.50% at 100 µg/mL). Nanoparticle formation was verified by surface plasmon resonance at 405 nm (UV-Vis), chitosan-metal coordination (FTIR), face-centered cubic structure with Cu incorporation (XRD, crystallite size 28 ± 1.4 nm), and quasi-polygonal morphology (TEM, 50.3 ± 12.8 nm). Williamson-Hall analysis indicated low compressive microstrain (ε = - 0.323 × 10⁻³) and a strain-corrected crystallite size of 51.7 nm, consistent with TEM. Antimicrobial assays against Escherichia coli O157:H7 and Staphylococcus aureus showed inhibition zones of 26.33 ± 0.58 mm and 22.50 ± 0.50 mm, with minimum inhibitory concentrations of 0.156-0.312 mg/mL. This work demonstrates the potential of integrated waste-to-nanomaterial strategies for antimicrobial applications, highlighting the need for mechanistic studies, biocompatibility assessment, and scale-up evaluation.