A Review on Antibacterial Properties of Biologically Synthesized Zinc Oxide Nanostructures

Anti-bacterial activity of biologically synthesized zinc oxide (ZnO) nanostructures has engrossed great attention around the globe due to distinctive nanotechnological applications. Biogenic ZnO nanostructures have prominent anti-bacterial properties as compared to bulk because small sized nanostructures exhibit larger surface area leading to improved particle surface-reactivity. This study reveals that biologically synthesized ZnO nanostructures are bio-compatible, stable and have longer shelf life due to presence of phytochemicals which acts as stabilizing and capping agents during synthesis process. The anti-bacterial mechanism of ZnO nanostructures includes production of reactive oxygen species (ROS) such as hydrogen peroxide H2O2, OH− and O2−2. The ROS provides major toxicity mechanism which includes destruction of cell wall due to interaction of ZnO nanostructures. Sometimes, ZnO nanostructures have increased anti-bacterial activity due to surface imperfections and ROS generation in dark. Interaction between ZnO nanostructures and bacterial cell causes mitochondrial weakness, intra-cellular outflow, and oxidative stress which eventually inhibits bacterial growth and kills the whole cell. This review describes anti-bacterial activity of biologically synthesized ZnO nanostructures by previously reported literature and tests used to examine anti-bacterial activity, influence of UV illumination, ZnO unique features i.e. size, concentration, morphology, and defects. Furthermore, it also presents significant anti-bacterial applications of ZnO nanostructures particularly in food packaging industry, pharmaceutical industry and other health care applications.