A green and facile approach to durable antimicrobial coating of cotton with silver nanoparticles, whey protein, and natural tannin

Antimicrobial cotton textiles were fabricated via green synthesis of silver nanoparticles (AgNPs) from silver nitrate, using whey protein isolate (WPI) as both reducing agent and stabilizer. Natural tannin-rich extract from Xylocarpus granatum bark (XGBE) was used to form insoluble complexes with the WPI through hydrogen bonding and hydrophobic forces. Cotton fabrics were coated using one-step padding of the AgNP/WPI/XGBE mixture, followed by air drying. Both WPI and XGBE served as an excellent natural binder for AgNPs with cotton. Transmission electron microcopy showed the AgNPs to be almost spherical, with a mean diameter of 31 nm. Antimicrobial treatment did not significantly alter the original color of the fabrics at low AgNPs loadings. The coated fabrics showed strong and durable antibacterial activity against Staphylococcus aureus and Escherichia coli, with 99.99% bacterial reduction. Treatment with only 50 ppm of silver nitrate and WPI maintained more than 90% bacterial reduction after 50 washing cycles. In a test of antifungal properties, at least 203 mg silver per kilogram of fabric was required to suppress the growth of Aspergillus niger. In-vitro cytotoxicity testing demonstrated the antimicrobial treated fabrics to be non-toxic to L929 cells. Antimicrobial treatment did not have significant negative effects on the drapeability and tearing strength of the fabrics. This approach is very attractive in terms of the safety and biocompatibility of the raw materials, the simplicity of the synthesis and the coating process, and the antimicrobial effectiveness of the treated fabrics.