Sonochemical One-Step Synthesis of Polymer-Capped Metal Oxide Nanocolloids: Antibacterial Activity and Cytotoxicity

Abstract

Most antibacterial agents demand their action in the form of a liquid for compatibility and ease of use in biosystems, which are mainly composed of biological fluids. Controlling the colloidal stability of metal oxide nanocolloids, in parallel with minimizing the effect of using a large amount of surfactant on their biocidal activity and cytotoxicity, remains a challenge. Here, we address the stability of nanocolloids of ZnO and CuO in the presence of polymer surfactants and the influence of the surface capping on their antibacterial activity and cytotoxicity. The metal oxide nanoparticles (NPs) were synthesized sonochemically in a single step and tested against both Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus to validate their biocidal efficacy. Cytotoxicity studies were performed on human alveolar epithelial cells. Polyethylene glycol- and polyvinyl alcohol-capped NPs are observed to show the minimum cytotoxicity whereas polyethylene imine-capped and pristine metal oxide NPs are toxic to the mammalian cells. The cytotoxic and antibacterial properties of the stable nanocolloids displayed an inverse relation, highlighting the role and significance of the polymer capping. The nontoxic biocidal nanocolloids showed an effective antibacterial efficacy of 99.9% in 2 h.

Figure 1

Representative XRD profiles of (a) ZnO-capped with (i) PEI, (ii) PEG, and (iii) PVA and (iv) pristine and (b) CuO-capped with (i) PEI (ii) PEG, and (iii) pristine.

Figure 2

Zeta potentials for polymer-capped ZnO and CuO NPs.

Figure 3

Antibacterial activity of pristine and surfactant-stabilized nanocolloids of (a) ZnO and (b) CuO against E. coli.

Figure 4

Antibacterial activity of pristine and surfactant-stabilized nanocolloids of (a) ZnO and (b) CuO against S. aureus.

Figure 5

ESR spectra demonstrating (a) relative ROS production by ZnO and CuO NPs in the surfactant matrix and (b) integrated area depicting signal intensity of the generated ROS.

Figure 6

TEM images of the colloidal NPs: (a) CuO–PEG and (b) ZnO–PVA. Inset shows the low magnification images of the samples.

Figure 7

Cytotoxicity of pristine and surfactant-stabilized nanocolloids. Cell viability was measured by the [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] MTT assay. (a,b) Effects of ZnO and CuO NPs after 3 h exposure and (c,d) effects of ZnO and CuO NPs after 24 h exposure.