Green Fabrication of Cobalt Oxide Nanoparticles by Bacillus megaterium and Their Antibacterial Activities

Cobalt oxide nanoparticles (Co₃O₄-NPs) have many applications, and today, the biosynthesis of these nanoparticles is preferred over other methods in terms of the advantages associated with it. Biosynthesis of nanoparticles (NPs) using bacteria is a novel and environmentally safe method that can be used in numerous biomedical applications. In recent years, many studies were performed on the antibiotic effects of nanoparticles and nano coatings on pathogenic agents. The purpose of this study is to determine which concentrations of cobalt oxide nanoparticles produced by Bacillus megaterium are most effective against Gram-positive and Gram-negative pathogenic bacterial strains, namely Staphylococcus aureus (S. aureus) and Pseudomonas aeruginosa (P. aeruginosa), respectively. The best concentration of cobalt oxide nanoparticles synthesized in this biological method at room temperature was selected from four concentrations of cobalt chloride hexahydrate salt after the characterization of nanoparticles. The necessary characteristics were investigated, such as a UV-Vis spectrometer to confirm synthesis, field emission scanning electron microscope to study the structure of nanoparticles, and X-ray diffraction for bell phase structure properties. The identification of generated nanoparticles, Fourier transform infrared spectroscopy to determine the number of components, X-ray energy dissociation spectroscopy for structural analysis and analysis of elements in the sample, vibrating sample magnetometer, and dynamic light scattering were performed to evaluate the hydrodynamic size of nanoparticles and evaluate the zeta potential to determine the surface charge. It is worth mentioning that the biosynthesis of cobalt oxide nanoparticles has not yet been performed by Bacillus megaterium. Cobalt oxide nanoparticles generated by Bacillus megaterium at an 80-mM salt concentration exhibited the highest quality. In conclusion, the assessment of cobalt oxide nanoparticles’ antibacterial activity was conducted utilizing the agar disk diffusion method. The cobalt oxide nanoparticles had a significant effect and more antibacterial properties on pathogens, especially Gram-negative, than the common antibiotics used in this study.