The influence of the crystalline nature of nano-metal oxides on their antibacterial and toxicity properties

The antibacterial properties of nano-metal oxides (ZnO, CuO) are based on the formation of reactive oxygen species (ROS). This work reveals that the antibacterial properties of these nano-metal oxides are strongly dependent on their crystalline structure. The antibacterial activity of the nanooxides was tested against four types of bacteria that commonly cause nosocomial infections. The sonochemical method was applied not only for synthesis of nanooxides but also to their coating on textiles. The antibacterial properties of textiles coated with commercial and sonochemically prepared nano-metal oxides were evaluated and compared. The toxicity was evaluated on human lung cells and amphibian embryos, as representative models for inhalation and aquatic toxicology. The sonochemically prepared metal nanooxides are better antimicrobials than commercially available metal oxides with the same particle size range. It was found that the crystallites which have more defects and less organized structure are more toxic. The formation of ROS was studied by electron spin resonance (ESR) measurements for both the sonochemically prepared and commercial samples of ZnO/CuO nanoparticles. A significant increase in the production of radical species was found in the more defective, sonochemically prepared samples, as compared to the commercial ones. Since modulation of the nanoparticle defects influenced their toxicity, the possibility of engineering safer nano-antibacterials is indicated.