Green synthesis of nano silver by tea extract with high antimicrobial activity

Abstract

In this study, a facile synthetic pathway was proposed to fabricate silver nanoparticles by using tea extract as reducing agent and stabilizer to reduce silver nitrate, which was further evaluated for the antimicrobial activity against bacterium (Escherichia coli) and pathogenic fungus of tea (Pseudopestalotiopsis theae). The average particle size of silver nanoparticles is 15.41 nm by X-ray diffraction (XRD) and Scherrer equation, the morphology is relatively regular and well dispersed by scanning electron microscope (SEM) and transmission electron microscope (TEM), the zeta potential is −13.91 ± 0.89 mV and the aggregate particle size distribution in water is around 773.49 nm. In addition, the synthesized nano silver had good antimicrobial effect on Pseudopestalotiopsis theae (P. theae) and Escherichia coli (E. coli), and the inhibition ratio was 96.05% and 61.87%, respectively. And the reaction of silver nanoparticles with bacteria and fungi could not be driven by the electrostatic interactions, but might by intermolecular forces. This study provides a facile and effective method for the preparation of nano silver, and broadens the application of nano silver in antimicrobial agent.