Biosynthesis, Characterization and Biological Activities of Silver Nanoparticles from Benth. Methanolic Leaf Extract.

This study reports the biosynthesis of silver nanoparticles (AgNPs) using methanolic leaf extract of Benth. (Patchouli) as a reducing agent, and their potent biological (antibacterial, antioxidant and anticancer) activities. The extract when exposed to silver nitrate reduced silver ions to form crystalline AgNPs within 1 h of incubation at room-temperature. UV-visible spectra showed a sharp surface plasmon resonance (SPR) at around 430 nm for the biosynthesized AgNPs and the XRD pattern indicated the crystalline planes of the face centered cubic silver. The FE-SEM analysis revealed the occurrence of predominant spherical shaped AgNPs with a huge disparity in their particle size distribution with an average size of 25 nm, while, the FTIR data confirmed the bio-reduction and capping of AgNPs by several phytocompounds present in the methanolic leaf extract. AgNPs effectively inhibited the growth of all the tested human pathogenic bacterial strains (, and ), while, the methanolic leaf extract failed to inhibit the growth of and . AgNPs showed the highest free radical scavenging activity (79.0 ± 0.76%) compared to methanolic leaf extract (68.3 ± 0.68%) at 100 g/ml. Further, the cytotoxicity study using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) confirmed that AgNPs successfully inhibited the human colon adenocarcinoma cell line (HT-29) in a dose dependent manner. At higher concentrations (500 g/ml), only 4% of cells survived after 72 hrs of exposure with IC value of 120 g/ml. Thus, these findings offer a new source of biomolecules with diverse biological activities.