Green synthesis of silver nanoparticles using leaf extracts of Mentha arvensis Linn. and demonstration of their in vitro antibacterial activities

ABSTRACT

Abstract A study was carried out to synthesize silver nanoparticles (Ag-NPs) using plant extracts and to explore their pharmaceutical application as antibacterial agents. Dried leaves of Mentha arvensis Linn. were powdered and extracts were prepared using three different organic solvents. Preliminary screening on antibacterial activity by agar well diffusion method indicated that the methanolic extract possessed higher potential than the other two. Phytochemical analysis of the leaf extract revealed that it possesses tannins, steroids, terpenoids and flavonoids. Ag-NPs prepared using this extract were of spherical to cuboidal shape ranging in size from 40 to 70 nm. It retained essential chemical groups and had the required surface plasmon resonance. Further to the antimicrobial assay, the Ag-NPs, in contrast to the whole methanolic leaf extract, showed better (100% vs. 80%) bactericidal activity against the indicator organisms. The zones of growth inhibition for gram positive bacteria ranged between 14±0.6 and 23±0.3, while it was between 12±0.6 and 22±0.2 for gram negative bacteria. The Ag-NPs presented the minimum inhibitory concentration values of 250 µg/mL for gram positive bacteria and 250 - 500 µg/mL for gram negative bacteria. These findings suggest that the natural compounds present in M. arvensis L. possess the potency to facilitate the synthesis and antibacterial action of Ag-NPs.