Strong larvicidal potential of silver nanoparticles (AgNPs) synthesized using Holarrhena antidysenterica (L.) Wall. bark extract against malarial vector, Anopheles stephensi Liston

The present study highlights the strong larvicidal potential of silver nanoparticles (AgNPs) synthesized using bark extract of Holarrhena antidysenterica against third instar larvae of Anopheles stephensi over the other bark extract prepared in chloroform, hexane, ethyl acetate, methanol, aqueous and acetone individually. AgNPs were prepared by mixing of 90 ml of silver nitrate (AgNO3) with 10 ml of aqueous bark extract of H. antidysenterica. Optimization of various physical parameters such as temperature, pH, time duration and AgNO3 concentrations was done and 1 mM of AgNO3, 7.5 pH, 50 2 degrees C temp and time 120 min proved optimum for best synthesis of AgNPs. Characterized of AgNPs was done by ultraviolet visible spectroscopy (UV-vis), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscope (FE-SEM) and transmission electron microscope (TEM). XRD pattern of such AgNPs revealed characteristics Bragg's reflection peaks at (38.34) 111, (44.54) 200, (64.36) 220 and (76.9) 311 lattice planes indicating the crystalline nature of biologically synthesized AgNPs. FT-IR analysis of AgNPs exhibited the presence of functional groups of various compounds including phenols, alcohols, amine, amide which were responsible for the reduction and capping of AgNPs. The FE-SEM and TEM images showed that most of the AgNPs were spherical, hexagonal and triangular in shape varying from 40 to 60 nm in size. Larvicidal activity of these AgNPs and bark extracts prepared in different solvents such as hexane, ethyl acetate, methanol, water and chloroform were tested separately against the A. stephensi larvae for 24 h. Maximum larval mortality was seen with bark extract synthesized AgNPs having LC50, and LC90 value of 2.672 ppm and 4.482 ppm, respectively compared to chloroform, hexane, ethyl acetate, methanol, water and acetone bark extracts where the LC50 values were 3.0, 31.56, 41.92, 96.40,121.53 and 1.91E3 ppm, respectively. Incidentally, AgNPs proved non-toxic against the non target organism, Mesocyclops thermocyclopoides. GC-MS analysis of bark extract identified 41 compounds having a range of activities which might have helped in the bio-reduction of AgNPs. These AgNPs have tremendous applications in pharmaceutical and biomedical industries such as cancer therapies, targeted drug delivery, as antiseptic agents and as an imaging agent. (C) 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.