Role of salt precursors for the synthesis of zinc oxide nanoparticles and in imparting variable antimicrobial activity

Synthesis of nanoparticles (NPs) having unique potentials and properties is of great importance in nanotechnology. The NP synthesis techniques may include the wet chemistry to microbial incubation reduction methods. This work reports generation of ZnO NPs by identical preparation including incubation of different zinc salts i.e. zinc acetate, zinc chloride and zinc sulphate as precursors with cell free extracts of Bacillus circulans MTCC 7906 (Bc7906) and Pleurotus florida (Pf). The synthesized NPs exhibited variation in their absorption peaks in UV-Vis spectra which appeared at 275 nm, 325 nm and 375 nm with P. florida for the three salt precursors respectively while the Bc7906 generated ZnO NPs showed peaks between 300-350 nm. A variation in ZnO NP morphology ranged from 50 to 120 nm in size and spherical, oval, cylindrical to trigonal anisotropic in shape by transmission EM. Further, the rough and corrugated surface topography of ZnO NPs was observed in Scanning EM. The % weight for Zn element surface composition as recorded by SEM-EDS was observed to be highest for zinc acetate (2.34%) and zinc sulphate (7.54 %) on microbial synthesis from Bc7906 and Pf respectively. The antimicrobial potential of the synthesized ZnO NPs on human pathogenic and plant beneficial bacteria was tested and it was observed to be highest for microbially synthesized ZnO NPs using zinc acetate (15 mm) and zinc sulphate (14 mm) as salt precursors @ 10 ppm. This is the first report on differential antimicrobial behavior of ZnO NPs on human pathogenic and plant beneficial microbes