Self-induced transformation of raw cotton to a nanostructured primary cell wall for a renewable antimicrobial surface

Herein, raw cotton is shown to undergo self-induced transformation into a nanostructured primary cell wall. This process generates a metal nanoparticle-mediated antimicrobial surface that is regenerable through multiple washings. Raw cotton, without being scoured and bleached, contains noncellulosic constituents including pectin, sugars, and hemicellulose in its primary cell wall. These noncellulosic components provide definitive active binding sites for the in situ synthesis of silver nanoparticles (Ag NPs). Facile heating in an aqueous solution of AgNO₃ activated raw cotton to produce Ag NPs (ca. 28 nm in diameter and 2261 mg kg^-1 in concentration). Compared with scoured and bleached cotton, raw cotton requires lower concentrations of AgNO₃-ten times lower for Klebsiella pneumonia and two times lower for Staphylococcus aureus-to achieve 99.9% reductions of both Gram-positive and Gram-negative bacteria. The Ag NPs embedded in the primary cell wall, which was confirmed via transmission electron microscopy images of the fiber cross-sections, are immobilized, exhibiting resistance to leaching as judged by continuous laundering. A remarkable percentage (74%) of the total Ag NPs remained in the raw cotton after 50 laundering cycles.