Facile preparation and antibacterial activity of zinc oxide nanobullets

Bacterial infections and emergence of many multidrug resistant bacterial pathogens are serious threats to human health. Nanostructured metal oxides are now used as antibacterial additives in various products of everyday usage, but their mode of antibacterial action still remains unclear. ZnO nanobullets were synthesized using a surfactant-free and template-free simple chemical route and well characterized by using FESEM, TEM, HRTEM, XRD, Raman and UV-vis spectroscopy. FESEM and TEM revealed bullet-shaped ZnO nanostructures with average size 50 nm. XRD analysis confirmed hexagonal wurtzite structure of ZnO nanobullets with crystallite size of 24 nm. We explored the antibacterial effects of ZnO nanobullets on gram-negative (Escherichia coli) and grampositive (Bacillus oceanisediminis), and investigated the underlying mechanism using morphological analysis by SEM, ROS scavenging by histidine, thiobarbituric acid reactive species (TBARS) assay, analysis of potassium ion leakage and Bradford assay. Our results demonstrated that ZnO nanobullets efficiently inhibited the growth of both Escherichia coli and Bacillus oceanisediminis bacteria. Furthermore, various biochemical and molecular assays have provided evidence that the strong antibacterial action of ZnO nanobullets can be attributed to ROS induced oxidative stress resulting in enhanced lipid peroxidation and cell membrane damage, which subsequently caused protein leakage. In summary, our results show that ZnO nanobullets exhibit a strong antibacterial activity against both Escherichia coli and Bacillus oceanisediminis under ambient lighting, which is exciting for practical applications.