Silver nanoparticle synthesis by Acalypha wilkesiana extract: phytochemical screening, characterization, influence of operational parameters, and preliminary antibacterial testing

Single pot green synthesis of silver nanoparticles (AgNPs) was successfully carried out using medicinal plant extract of Acalypha wilkesiana via bottom-up approach. Five imperative operational parameters (pH, contact time, concentration, volume ratio and temperature) pivotal to the synthesis of silver nanoparticles were investigated. The study showed pH 9, 90 min contact time, 0.001 M Ag+ concentration, volume ratio 1:9 (extract: Ag+ solution), and temperature between 90 - 100 degrees C were important for the synthesis of Acalypha wilkesiana silver nanoparticles (AW-AgNPs). Phytochemical screening confirmed the presence of saponins, flavonoids, phenols and triterpenes for A. wilkesiana. These phytomolecules served as both capping and stabilizing agent in the green synthesis of silver nanoparticles. AW-AgNPs was characterized by UV-Vis Spectroscopy, Fourier Transform Infrared (FTIR) Spectroscopy and Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Energy Dispersive X-ray (EDX). The surface Plasmon resonance (SPR) was observed at 450 nm which is a characteristic absorbance region of AW-AgNPs formation as a result of the collective oscillation of free electron of silver nanoparticles. FTIR Spectroscopy confirmed the presence of functional groups responsible for bioreduction of Ag+. SEM and TEM results confirmed a well dispersed AW-AgNPs of spherical shape. EDX shows the elemental distribution and confirmed AgNPs with a characteristic intense peak at 3.0 keV. AW-AgNPs showed significant inhibition against selected Gram negative and Gram positive prevailing bacteria. AW-AgNPs can therefore be recommended as potential antimicrobial and therapeutic agent against multidrug resistant pathogens.