Green synthesis of silver nanoparticles using Ocimum gratissimum leaf extract: characterization, antimicrobial activity and toxicity analysis

The present study reports the optimization of various parameters for green synthesis of silver nanoparticles using aqueous leaf extract of Ocimum gratissimum. The effects of various parameters such as concentration of AgNO3, ratio of AgNO3 to extract, pH and incubation time were studied in order to optimize the synthesis process. 5 mM AgNO3, 1:0.06 ratio of AgNO3 to O. gratissimum leaf extract, pH 9.0 and incubation of reaction mixtures for 24 h were found to be the optimum parameters for synthesis of silver nanoparticles (AgNPs). The synthesized AgNPs were characterized by UV–visible absorption spectroscopy, scanning electron microscopy and transmission electron microscopy. The nature of the reducing and capping agents in the leaf extract was determined using Fourier transform infrared spectrometer analysis. Furthermore, AgNPs showed higher antimicrobial activity against the Gram negative (Escherichia coli, Klebsiella pneumoniae) in comparison to the Gram positive bacteria (Staphylococcus aureus, Bacillus subtilis and Micrococcus luteus). In addition to this, AgNP containing solution was subjected to toxicity analysis using seeds of Moong Bean (Vigna radiata). It was found that seeds treated with AgNP solutions showed better rates of germination and oxidative stress enzyme activity was at par with the control levels. This study demonstrates that O. gratissimum leaf extract can be used for production of AgNPs with potential antibacterial activity. Future research is warranted on the investigation of detailed mechanism of their antimicrobial activity, uptake and translocation in plants.