Bacterial cell permeability study by metal oxide and mixed metal oxide nanoparticles: analysis of the factors contributing to the antibacterial activity of nanoparticles

In this work, we investigate the nanoparticle-cell wall interaction by NiO and mixed metal oxide CuO-NiO nanoparticles. We have synthesized and characterized the nanoparticles using XRD, FESEM, EDS, UV vis. spectroscopy, FTIR, Zeta, and TEM analysis in our previous work. Furthermore, a preliminary antibacterial study showed that both the nanoparticles performed very well as antibacterial agents. In this extended work, we investigate the mechanism of interaction of NiO and CuO-NiO nanoparticles with S. aureus and E. coli cells as there are number of studies for antibacterial mechanism of CuO nanoparticles. The uptake of crystal violet dye in the outer bacterial membrane, the release of ss-galactosidase enzyme, and relative electric conductivity assay were used to investigate changes in the permeability and integrity of the cell membrane. Superoxide ions, which are produced intracellularly as ROS by nanoparticles, severely damage bacterial membranes. Zeta potential measurement, which resulted in surface charge neutralization, proved membrane instability. FTIR analysis was used to identify changes in the proteins, carbohydrates, and fatty acids that make up the chemical composition of cell surfaces. AFM imaging demonstrated extensive alteration of the nanomechanical and surface characteristics. Confocal microscopy examination supported the DNA fragmentation and nanoparticle-cell adhesion. Due to their enhanced antibacterial activity when compared to monometallic oxide nanoparticles, this study demonstrated that mixed metal oxides can be employed in the health and biomedical sectors.