Synthesis and characterization of zinc/iron oxide composite nanoparticles and their antibacterial properties

Inorganic metal oxides may serve as effective disinfectants, due to their relatively non-toxic profile, chemical stability and efficient antibacterial activity. Among metal oxide nanoparticles, zinc oxide demonstrates significant bacterial growth inhibition on a broad spectrum of bacteria, mainly by catalysis of reactive oxygen species (ROS) formation from water and oxygen. Aqueous suspensions of ZnO nanoparticles (ZnO nanofluids) are the preferred formulation for using the antibacterial agent in liquid phases and for the incorporation of the nanoparticles in different commercial products. However, ZnO nanoparticles in aqueous media tend to aggregate into large flocculates, due to their hydrophobic nature, and thus do not interact with microorganisms effectively. In this study, zinc oxide was combined with iron oxide to produce magnetic composite nanoparticles with improved colloidal aqueous stability, together with adequate antibacterial activity. For this purpose, the Zn/Fe oxide composite nanoparticles were synthesized by basic hydrolysis of Fe²⁺ and Zn²⁺ ions in aqueous continuous phase containing gelatin. The obtained composite nanoparticles were composed of iron oxide, zinc oxide and zinc ferrite phases. The effect of the weight ratio [Zn]/[Fe] of the composite nanoparticles on their properties (composition, size, magnetic behavior and colloidal stability) was elucidated. The antibacterial activity of these nanoparticles was tested against Staphylococcus aureus and Escherichia coli and was found to be dependent on the weight ratio [Zn]/[Fe], i.e., the higher the ratio, the higher the antibacterial activity. In addition, the activity against Staphylococcus aureus was significantly higher than that observed against Escherichia coli.