Advanced freeze–thaw production of fungal chitosan and its Ag–Cu nanocomposite: enhanced antimicrobial activity and in vitro cytotoxicity evaluation
TL;DR
The observation therefore demonstrate that in addition to being an effective platform for functionalization and stabilization of biopolymer and Ag–Cu composite, freeze–thaw-derived fungal chitosan is a sustainable alternative to conventional chitosan sources.
Abstract
Antimicrobial resistance continues to undermine the effectiveness of conventional treatments and so, in this study, fungal chitosan was produced from Pleurotus ostreatus through chitin extraction followed by freeze–thaw-assisted deacetylation and subsequent stabilization and capping of Ag–Cu nanoparticles. The as-synthesized nanocomposites were characterized and evaluated for their antimicrobial and cytotoxic properties. Fourier-Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDX), elemental mapping, and zeta potential analysis confirmed successful formation of the fungal chitosan and Ag–Cu nanocomposite. Average crystallite sizes of 9.49, 30.60, 22.25, and 23.74 nm were obtained for the reference chitosan (RCS), synthesized chitosan (OCS), chitosan–Ag–Cu (OCS3) composite, and Ag–Cu (NCS2) nanoparticles respectively. Microscopic and elemental analyses revealed a compact fibrillar and heterogeneous porous morphology together with homogeneous elemental distribution in the composite, confirming successful incorporation of Ag and Cu throughout the chitosan matrix indicating effective stabilization of the metallic phase. All the formulations exhibited positive zeta potential values, suggesting favorable colloidal stability. Biological evaluation demonstrated showed that OCS3 exhibited strong activity against Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, Enterococcus faecium NJ-1, Staphylococcus aureus ATCC 29213, and Candida albicans ATCC 90028, outperforming fungal chitosan alone. The L929 fibroblasts and MCF-7 breast cancer cells cell-culture studies further revealed pronounced differences in selectivity and cytotoxicity of the formulations. NCS2 gave the most balanced combination of antiproliferative activity and biological discrimination, unlike the OCS which showed the most favorable selectivity profile and OCS3 displayed the highest cytotoxic potency but limited selectivity toward cancer cells. The observation therefore demonstrate that in addition to being an effective platform for functionalization and stabilization of biopolymer and Ag–Cu composite, freeze–thaw-derived fungal chitosan is a sustainable alternative to conventional chitosan sources.