Morphology-dependent antimicrobial activity of Cu/CuxO nanoparticles.

Cu/CuxO nanoparticles (NPs) with different morphologies have been synthesized with glucose as a reducing agent. The X-ray diffraction and Scanning electron microscopy imaging show that the Cu/CuxO NPs have fine crystalline peaks with homogeneous polyhedral, flower-like, and thumbtack-like morphologies. Their antimicrobial activities were evaluated on inactivation of Escherichia coli using a fluorescence-based live/dead staining method. Dissolution of copper ions from these NPs was determined. Results demonstrated a significant growth inhibition for these NPs with different morphologies, and the flower-like Cu/CuxO NPs were the most effective form, where more copper ions were dissolved into the culture media. Surface free energy calculations based on first-principle density functional theory show that different crystal facets of the copper NPs have diverse surface energy, indicating the highest reactivity of the flower-like NPs, which is consistent with the results from the dissolution study and antimicrobial activity test. Together, these results suggest that the difference between the surface free energy may be a cause for their morphology-dependent antimicrobial activity.