Synthesis, characterization and antimicrobial activity of Alstonia scholaris bark-extract-mediated silver nanoparticles

Nanobiotechnology has been emerging as an interdisciplinary act which converges materials and living organisms at nanoscale and proved to be one of the potential tools in nanotechnology to address some of the critical problems. Production of biogenic metallic nanoparticles using microorganisms and other living organisms including plants is been an attracting research activity. Herein, we report the synthesis of silver nanoparticles (AgNPs) using the bark extract of Alstonia scholaris, one of the most important medicinal plants and their promising antimicrobial activity. Stable AgNPs were formed by treating 10 % of A. scholaris bark extract with the aqueous solution of AgNO3 (1 mM). The formation of AgNPs was confirmed by UV–visible spectroscopic analysis and recorded the localized surface plasmon resonance of Ag- NPs at 432 nm. Fourier transform infrared spectroscopic analysis revealed that primary and secondary amine groups in combination with the proteins present in the bark extract are responsible for the reduction and stabilization of the AgNPs. X-ray diffraction micrograph indicated the facecentered cubic structure of the formed AgNPs, and morphological studies including size (average size 50 nm) were carried out using transmission electron microscopy. The hydrodynamic diameter (111.7 nm) and zeta potential (-18.9 mV) were measured using the dynamic light scattering technique. The antimicrobial activity of A. scholaris bark-extract-mediated AgNPs was evaluated (in vitro) against fungi, Gram-negative and Gram-positive bacteria using disc diffusion method.