Biological Effects of Freshly Prepared and 24-h Aqueous Dispersions of Copper and Copper Oxide Nanoparticles on E. coli Bacteria

Abstract

Copper and copper oxide nanoparticles are promising candidates for the role of “new antibiotics.” However, characteristics of their effect on microorganisms, depending on the nature of the dispersion medium and the time of storage of suspensions, have not been thoroughly studied, which limits the possibilities of application in practice. A comparative evaluation of the effects of freshly prepared and 24-h suspensions of copper and copper oxide nanoparticles (100 nm in size) on E. coli bacteria using the bioluminescence test is carried out. Distilled water and saline are used as dispersion media; the nanoparticle concentration is 1–0.0001 g/L. Significant differences in the antibacterial properties of freshly prepared suspensions of copper and copper oxide nanoparticles are revealed. Colloidal solutions of copper oxide in all studied concentrations have a significant toxic effect in both types of dispersion media (the survival rate of bacteria is less than 20–40%). An antibacterial effect is observed only at 1 g/L of copper nanoparticles (survival is less than 50%) in fresh aqueous dispersions and at 0.01–1 g/L in solutions based on saline (survival rate is 15–75%); i.e., in this case, the role of the dispersion medium is essential. The storage of solutions for 24 h results in a significant decrease in the toxicity of the colloid systems of copper oxide nanoparticles both in water and saline, while the antibacterial effect of suspensions of copper nanoparticles remains almost the same, regardless of the medium type. These phenomena can be caused by changes in the stability of colloidal systems accompanied by the aggregation of nanoparticles. These results indicate the importance of taking into account the nature of the dispersion medium and the time of storage of suspensions of copper-based nanoparticles for their efficient use as antimicrobial agents.