Chitosan/copper nanocomposites: Correlation between electrical and antibacterial properties.

Correlation between electrical and antibacterial properties of chitosan/copper nanocomposites (CS/CuNPs) is investigated. We aim at achieving the minimum CuNPs concentration in a CS-matrix while keeping high antibacterial activity. UV-vis, TEM and XRD measurements confirms the formation of polygonal metallic CuNPs (ca. 30-50 nm). Interactions between NH2/OH groups of CS and CuNPs were determined by FTIR and XPS suggesting Cu chelation-induced mechanism during the CuNPs formation. DC electrical conductivity measurements reveals a percolation threshold at CuNPs volumetric concentration of ca. 0.143%. Antibacterial assays against Gram-positive bacteria and DC measurements helps correlate the antibacterial potency to the electron transfer between the negatively charged bacteria and CuNPs. Our study suggests that nanocomposite's maximum antibacterial activity is obtained below the electrical percolation threshold at extremely low CuNPs concentrations; this fact may prove useful in the design of nontoxic nanocomposites for biomedical applications.