Effect of NaOH concentration on antibacterial activities of Cu nanoparticles and the antibacterial mechanism.

A series of Cu nanoparticles (NPs) have been prepared by a facile hydrothermal method at 180 °C using different concentrations of NaOH solutions and characterized by XRD, SEM, TEM and FT-IR spectra. Their antibacterial activities were assessed by means of Gram-positive S. aureus and Gram-negative E. coli bacteria, where various dosages (3, 5, 7, 10 mg) of the antibacterial agents were applied, and compared with that of the commercial CuSO salt. The antibacterial mechanism was explored based on series of control experiments. The results show that the NaOH concentration affects the crystallinity, crystal size and surface hydroxyl content of the Cu NPs, which significantly influence the antibacterial activities. Compared to the commercial CuSO salt, the four Cu samples prepared using no <4 mol L of NaOH display excellent antibacterial activities with low concentrations of copper leachates, which is great beneficial to the practical applications. The experimental results support that the highly reactive and soluble copper species in the antibacterial system of the Cu NPs is a Cu (II)-peptide complex, but not free Cu ions.