Synthesis, characterization, toxicological and antibacterial activity evaluation of Cu@ZnO nanocomposites

Abstract Cu@ZnO is an important class of material with applications as catalysts, photocatalysts, optoelectronic devices and antimicrobial agents. Because of its potential for large-scale applications and its high redox activity, detailed examination of the properties and risk assessment of this class of materials should be performed. In this work, Cu@ZnO composites were synthesized using a two-step procedure. ZnO crystalline nanostructured materials were prepared within minutes by a solvothermal microwave-assisted method. Deposition of copper nanoparticles on the surface of ZnO was conducted by reduction of Cu2+ in ethylene glycol (EG). Copper nanoparticles with different morphologies (needle-like and spheres) were deposited on the surface of ZnO. The antibacterial activity of Cu@ZnO composites was evaluated using E. coli and S. aureus as model organisms. The Minimal Inhibitory Concentration (MIC) and Minimal Bactericidal Concentration (MBC) were evaluated for Cu@ZnO composites under visible light radiation (VLR) and in the dark (D). The composites exhibit antibacterial activity under VLR at low concentrations: 250 μg/mL and 750 μg/mL for E. coli, and 250 μg/mL and 500 μg/mL for S. aureus. Copper nanoparticles exert antibacterial activity and can be used to inhibit the growth of microorganisms in the absence of irradiation of Cu@ZnO material. Better antibacterial activity of Cu@ZnO material was achieved under radiation, demonstrating the synergic activity of Cu and ZnO materials for disinfection. Toxicity of the material was assessed towards Daphnia magna (D. magna) and Lecane papuana (L. papuana). Composites exert toxicity at lower concentrations than ZnO, observing LC50 values for L. papuana of 79.30 ± 6.70 μg/mL, and 5.59 ± 0.46 μg/mL for ZnO and Cu@ZnO, respectively. For D. magna, a LC50 of 9.66 ± 1.22 μg/mL (Cu@ZnO) was observed. Although Cu@ZnO can be considered as potential candidate for the development of efficient antibacterial agents, its antibacterial activity is achieved at doses that can be harmful to aquatic invertebrates. Thus, its application should avoid its entry to aquatic environments.