Investigating morphology-dependent antibacterial property of ZnO nanoparticles and developing an insight into oxidative stress generation and cellular response

Abstract

In this work, morphology-dependent antibacterial property of zinc oxide nanoparticles (ZNPs) has been studied and an attempt has been made to investigate the reactive oxygen species generation potential of these nanoparticles. The antibacterial properties of ZnO nanorods with two different sizes have been quantitatively studied and their Minimum Inhibitory Concentration (MIC) has been determined against E.coli, a gram negative bacteria. It has been observed that ZNPs with smaller size exhibit better bacteriostatic and bactericidal properties. Furthermore, optical analysis has revealed that the smaller nanoparticles having greater efficiency to inhibit cell growth have higher density of surface defects and greater availability of free electrons and holes which leads to the generation of reactive oxygen species (ROS). To develop an insight into the oxidative microenvironment and the consequential cellular response, we have done the transcriptional analysis of oxidative stress gene sodA in ZNPs treated bacterial samples. Expression profile of the gene has been found to be ZNPs concentration dependent. An increase in the concentration of nanoparticles till MIC increased the expression level in a concentration dependent fashion. However beyond the MIC, the expression level of the gene is unexpectedly down-regulated reflecting the detrimental effect of higher levels of ROS on cellular components and metabolic activities. Thus through this study, we have tried to investigate the correlation between the surface morphology of ZNPs, production of ROS, growth-inhibiting activity and cellular response in this condition.