Zinc oxide nanomaterials have sought considerable biomedical applications. The varying grain sizes of zinc oxide nanoparticles
(ZnO NPs) were prepared by wet chemical precipitation method. Particle size and morphology of the as-prepared ZnO powders were
characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), UV-Visible spectroscopy, dynamic light scattering
and transmission electron microscope (TEM). The antimicrobial and cytotoxic activity of varying sizes of ZnO NPs was investigated
in gram negative microorganisms and in colo 320 human adenocarcinoma cancer cells. The relationship between physico-chemical
properties and oxidative stress response in cell viability and toxicology was determined. The zone of inhibition by nanoparticles ranged
from 18 mm to 22 mm. The estimated inhibitory concentration (IC50) values for different sizes of zinc oxide nanoparticles were calculated
as 156.25 µg.ml-1 for 15 nm ZnO NPs, 191.5 µg.ml-1 for 25 nm ZnO NPs and 225.3 µg.ml-1 for 38 nm ZnO NPs. Varying sizes of
ZnO NPs were partially dissolved to Zn species (Zn(dis)) in Roswell Park Memorial Medium (RPMI) and in milli-Q water. Maximum dissolution
of Zn species was observed in milli-Q water. According to the results of the present study, mechanisms of action and cellular
consequences resulting from varying sizes of ZnO NPs interactions with infectious microbes and cancer cells suggest that particle size
not exceeding 25 nm can be further improved with surface functionalization and loading anti-cancer and anti-bacterial agents.
Keywords: Zinc oxide nanoparticles, cancer, cytotoxicity, oxidative stress, antibacterial activity.
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