Size- dependent Antibacterial Activity of Cobalt Oxide Nanoparticles

One of the major health problems that has been showing up recently, was due to the emergence of new bacterial strains that posses resistant to common antibiotics, scientist find out that with the unique properties of nanoparticles, a nanoscale material ranging from 1-100 nm, it become possible to use them as alternative antibacterial agents, and the antibacterial effectiveness of several metal oxide nanoparticles has been proved, were cobalt oxide nanoparticles is among one of these metal nanoparticles that can be used as antibacterial agent. As it well known that nanoparticles behavior is strongly governed by the size and composition of the particles, in this study cobalt oxide nanoparticles were prepared by a simplified salt reduction method where variations in the preparation conditions lead to the production of cobalt oxide nanoparticles in different forms and different sizes, the nanoparticles alone, were three samples were obtained with an average sizes ranging from (25.25nm, 21.61nm, 20.19nm), and three nanoparticles samples stabilized in Tetra octyl ammonium bromide (TOAB) with average sizes ranging from (23.08 nm, 19.47 nm, and 19.03 nm), and nanoparticles samples stabilized in Polyvinylpyrrolidone (PVP) with average sizes ranging from (20.87 nm, 17.73 nm, and 17.09 nm). The antibacterial inhibitory and bactericidal effects of all prepared cobalt oxide nanoparticles samples with different sizes were examined against Gram-positive S. aureus and Gram-negative E. coli both reference bacterial strains and clinical bacterial isolates. The overall experimental results indicate that cobalt oxide nanoparticles appear to have a promising results as antibacterial inhibitory effects against tested microorganisms were its related inhibitory effects were varied depending on the variations in the type of tested microorganism were it was more inhibitory toward S. aureus more than toward E. coli. A significant different in size-dependence of antimicrobial activity was observed, in which the fine scale differences in size of the prepared cobalt oxide nanoparticles can alter their related antibacterial activity. Moreover, the usage of the reference and the clinical bacterial isolates showed the great need to be carful that the clinical isolates could have a more robust antibacterial resistance. Key words: cobalt oxide nanoparticles, Tetra octyl ammonium bromide, Polyvinylpyrrolidone, S. aureus, E. coli.