Hydrothermal duck-feather keratin as a reagent-free bioreductant and capping matrix for bioactive silver nanoparticles

Abstract The sustainable production of silver nanoparticles (AgNPs) from renewable biowaste would reduce environmental burden and expand green nanotechnology applications. This study reports a hydrothermal extraction route that avoids external chemical reductants, thereby enabling duck-feather keratin to function intrinsically as both a reducing and capping agent in the synthesis of stable, bioactive AgNPs. Extraction was verified using the Lowry assay and SDS–PAGE, confirming preservation of protein content needed for metal coordination. One-factor-at-a-time optimization identified pH 11, 70 °C, 30 mL extract per 1 mM Ag⁺ reaction, and a 24 h duration as optimal conditions, producing uniform spherical nanoparticles having an average (11 nm) with excellent dispersion and long-term optical stability. Characterization by UV–Vis, FTIR, XRD, and SEM–EDX confirmed Ag⁺ reduction, keratin capping, and crystalline face-centered cubic Ag formation. TGA–DTA showed improved thermal stability, while BET surface area increased from 1.55 to 6.32 m2·g⁻1 after nanoparticle incorporation, indicating enhanced mesoporosity. The synthesized duck-feather keratin silver nanoparticles (DFKSN) demonstrated strong antioxidant activity and potent antibacterial performance, with DDT, MIC, and MBC assays confirming both bacteriostatic and bactericidal effects against Gram-positive and Gram-negative bacteria. The nanoparticles also promoted cytocompatibility in human skin fibroblasts cell (HSF1184) at a dose of 3.0 mg.mL−1. These findings highlight hydrothermally processed keratin as a scalable, waste-valorizing route for sustainable and eco-friendly nanomaterial production.