Olive and green tea leaf extracts mediated green synthesis of silver nanoparticles (AgNPs): comparison investigation on characterizations and antibacterial activity

The aim of this study is to develop biogenic silver nanoparticles (AgNPs) using olive leaf (OL) and green tea leaf (GTL) extract with a green synthesis approach and to compare and evaluate the characteristics and antibacterial activity of synthesized AgNPs. Various parameters affecting AgNPs synthesis such as temperature, pH, reaction time, amount of reducing extract, and concentration of silver nitrate (AgNO3) were determined and optimized. Furthermore, the synthesized AgNPs were characterized by UV–visible (UV–vis) spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDX). The formation of AgNPs was observed by changing the color of the reaction medium from white to dark brown and significantly increased in the basic environment with the change of temperature. The antibacterial activity of synthesized AgNPs was compared with that of aqueous OL and GTL by agar well diffusion method. According to the results, the best inhibition zone for E. coli bacteria resulted in an increase from 7 to 11 mm in GTL-synthesized AgNPs, and an increase from 9 to 10 mm in OL-synthesized AgNPs. Thus, green-synthesized AgNPs showed good antibacterial activity at lower concentration.