Roles of silver nanoparticles adsorbed ions and nanoparticles' size in antimicrobial activity of biosynthesized silver nanoparticles

The present study demonstrates a green and cost-effective approach for production of stable silver nanoparticles (AgNPs) from persimmon ( Diospyros kaki) fruit extract for the first time. 2 mM of AgNO3, temperature of 70 degrees C and incubation time of 24 h were chosen as the optimum conditions to synthesize AgNPs with a very high yield (>99.99%). Persimmon-AgNPs' characterization showed a narrow UV-vis peak at 411 nm with mean size of 20.7 +/- 9.1 nm. The negative zeta potential (-25.50 +/- 0.59 mV) revealed that high amounts of negatively charged biomolecules coated the surface of AgNPs and prevented them from aggregation through electrostatic repulsion. We further found that persimmon-AgNPs possessed a desirable stability against low pH values and high salinity concentrations when compared with Citrus maxima-mediated synthesized AgNPs. Furthermore, biosynthesized AgNPs exhibited a weak influence on the growth of bacteria (e.g., Escherichia coli and Staphylococcus aureus) and plant pathogens (like Fusarium oxysporum and Verticillium dahliae). For more investigation, a direct comparison among antimicrobial abilities of persimmon, Citrus maxima and Chenopodium aristatum mediated AgNPs was conducted, and the results demonstrated that negligible amounts of AgNPs absorbed Ag+ ions in persimmon-AgNPs as well as the relatively large size hindered their antimicrobial activity.