Antimicrobial Activity of Chemical, Thermal and Green Route-Derived Zinc Oxide Nanoparticles: A Comparative Analysis

In this study, antimicrobial activity of zinc oxide (ZnO) nanoparticles (NPs) synthesized by different chemical, thermal and green routes were systematically investigated with an aim to determine which method yields the most efficient antimicrobial property. The methodologies employed in this study were sol-gel, thermal decomposition, precipitation and green synthesis routes. The physical and optical properties of synthesized ZnO NPs were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), ultraviolet–visible spectroscopy (UV-Vis) and fluorescence spectroscopy. The results of the XRD and SEM analysis indicated the size and shape of the particles, depending on synthesis methodology and calcination temperature. The optical properties of the ZnO NPs investigated using UV-Vis absorption and photoluminescence spectra were also depending on the synthesized route. The antimicrobial activity of the ZnO NPs was tested against gram-negative bacteria (E. coli, P. aeruginosa and S. typhi), gram-positive bacteria (S. aureus and B. subtilis) and fungus (C. albicans) using agar-well diffusion method. Effects of size, shape of the crystal and concentration on the antimicrobial activity were investigated. The experimental results showed that the antimicrobial activity of ZnO NPs increased with decreasing size of the crystal. It was also found that the gram-positive bacteria were more sensitive to ZnO NPs than gram-negative bacteria and fungus. Interestingly, ZnO NPs synthesized using the green route showed more effective antimicrobial activity than those using the chemical or the thermal route.