Hydrothermally derived water-dispersible mixed valence copper-chitosan nanocomposite as exceptionally potent antimicrobial agent

We report, for the first time, a one-step hydrothermal (HT) process to design and synthesize water-dispersible chitosan nanoparticles loaded with mixed valence copper. Interestingly, this HT copper-chitosan biocompatible composite exhibits exceptionally high antimicrobial properties. A comprehensive characterization of the composite indicates that the hydrothermal process results in the formation of monodispersed nanoparticles with average size of 40 +/- 10 nm. FT-IR and Raman spectroscopic studies unveiled that the hydrolysis of the glycoside bonds as the origin of the depolymerization of chitosan. Furthermore, X-Ray Photoelectron Spectroscopy measurements confirmed the presence of mixed valence copper states in the composite, while UV-Vis and FT-IR studies revealed the chemical interaction of copper with the chitosan matrix. Hence, the extensive spectroscopic data provide strong evidence that the chitosan structure was rearranged to capture copper oxide nanoparticles. Finally, HT copperchitosan composite showed a complete killing effect when tested against both Gram negative (E. coli) and Gram positive (S. aureus) bacteria at metallic copper concentration of 100 mu g/ml (1.57 mM). At the same concentration, neither pure chitosan nor copper elicited such antimicrobial efficacy. Thus, we show that HT process significantly enhances the synergistic antimicrobial effect of chitosan and copper in addition to increasing the water dispersibility.