Vernonia cinerea (L.) Less. silver nanocomposite and its antibacterial activity against a cotton pathogen

Noble-metal nanomaterials are of particular interest today because of their applications in many areas, including agriculture. The latter topic is one of the most active areas of research in metal nanomaterials. Metal nanoparticles are traditionally synthesized by wet chemical techniques, in which the chemicals used are often toxic and flammable. We report here biosynthesis of silver nanoparticles using leaf extract of Vernonia cinerea (L.) Less. (Asteraceae). Treatment of aqueous solution of AgNO3 with V. cinerea leaf extract resulted in rapid formation of stable silver nanoparticles. The growth of nanoparticles was monitored by UV-Visible spectrophotometry complemented by characterization using transmission electron microscopy (TEM), X-ray diffraction analysis, and Fourier-transform infrared spectroscopy. A feasible mechanism for the formation of nanomaterial and the difference in the reduction time for silver nanoparticle synthesis is discussed. TEM analysis revealed the presence of polydisperse silver nanoparticles with average size of 5-50 nm. X-ray diffraction studies corroborated that the biosynthesized nanoparticles were crystalline silver. Furthermore, this green biogenic approach is a rapid and simple alternative to chemical synthesis. The biologically synthesized silver nanoparticles were found to be highly effective against Xanthomonas campestris pv. malvacearum (13.00 +/- A 0.58 mm) with minimum inhibitory concentration of 80 A mu g/mL. Hence, such biosynthesized silver nanoparticles can be used in control of cotton bacterial blight.