Surface cleanliness of hydrothermally grown zinc oxide microparticles compared to commercial nanoparticles

Zinc oxide (ZnO) nanoparticles are attractive candidates for application as antibacterial agents due to their effectiveness against antibiotic-resistant strains of both gram-positive and gram-negative bacteria. Despite this potential, applications are limited by fundamental gaps in current understanding of their underlying antibacterial pathways. ZnO microparticles are less often used in antibacterial research compared to ZnO nanoparticles due to the potential of nanoparticles for internalization into bacterial cells. Microparticles are nevertheless of interest as a research platform as their increased scale allows both the nonpolar and polar faces of the ZnO crystals to be distinguished. This in turn provides a useful platform to study surface interactions with bacteria, allowing for more targeted investigation of antibacterial mechanisms. Previous preliminary studies have indicated that hydrothermally grown ZnO microparticles exhibit comparable antibacterial activity to commercial ZnO nanoparticles further adding to their utility. The purpose of this research was to examine the surface cleanliness of ZnO microparticles in comparison to nanoparticles utilizing both scanning electron microscopy (SEM) as well as Fourier transform infrared spectroscopy (FTIR). The results of our experiments supported our hypothesis that there were no significant differences in the surface contamination of ZnO microparticles compared to nanoparticles. This supports the usage of ZnO microparticles as a viable platform for studying antibacterial mechanisms observed at the nanoscale knowing that in the absence of internalization effects the mechanism of antibacterial action across scales is intrinsic to ZnO and not a result of differing surface cleanliness.