Venonia amygdalina leaf extract - mediated redox synthesis of silver nanoparticles: Characterization and antimicrobial activity

Abstract

The synthetic process, type of precursor material, and the phytochemical materials involved in the biological synthesis of metal nanoparticles influence the properties of the resulting nanoparticles. The physicochemical attributes of synthesized nanoparticles, in turn, influence their applicability for various purposes, hence the need to standardize synthetic processes and characterize nanoparticle outputs for reproducibility and optimal utility. The objective of this study was to utilize bitter leaf (Vernonia amygdalina) extract in the synthesis of silver nanoparticles (AgNPs), characterize the nanoparticles, and then evaluate the same for antimicrobial activities. The V. amygdalina extract was produced by the soxhlet extraction process after the leaves were subjected to standard pre-extraction treatments using methanol as the extraction solvent. The solid extract was separated by rotary evaporation, and a predetermined quantity was mixed with 0.1 M silver nitrate solution under controlled concentration, temperature, and pressure. The resulting nanoparticles were characterized for morphological, optical, spectroscopic, and other physicochemical properties and then evaluated for antibacterial activities. The mean particle size, polydispersity index, and zeta potential of the nanoparticles were 74.231 ± 0.43 nm, 0. 645 ± 0.04, and 32.045 ± 0.054 mV, respectively. The Fourier transform infrared analysis suggested an association between the silver nanoparticles and the extract biomolecules, while x-ray diffraction showed particle crystallinity. The nanoparticles were effective against selected Gram-positive and Gram-negative bacteria. It was concluded that the procedure and materials used resulted in the synthesis of silver nanoparticles from the silver nitrate salt through a biogenic reduction process.