Green synthesis of silver nanoparticles from Heteropyxis natalensis leaf extract and their potential antibacterial efficacy

Silver nanoparticles (AgNPs) are sought after by many industries including food industries, heavy metal sensing, pharmaceutical, and textile. The present study reports on the biosynthesis of silver nanoparticles (AgNPs) and theirs antibacterial activity using a methanolic leaf extract of Heteropyxis natalensis, a native South African medicinal tree. The synthesised particles were characterised by ultraviolet visible spectroscopy (UV-vis), energy dispersive X-ray spectroscopy (EDX), high resolution transmission electron microscopy (HRTEM), and Fourier transform infrared spectroscopy (FTIR). A colour change of the reaction solution from yellow to brown preliminarily confirmed the presence of AgNPs, and a single absorbance peak at 422 nm, using UV-vis spectroscopy, was the indicative of AgNPs. While EDX revealed the presence of elemental silver in the sample, HRTEM identified spherical AgNPs ranging from 5-60 nm. Hydroxyls, alkynes, alkenes, alkanes, esters, and alkyl halides as possible capping agents of silver ions (Ag⁺) into AgNPs were identified by FTIR. In addition, AgNPs exhibited antibacterial efficacy against 5 strains of pathogenic bacteria: Escherichia coli, Staphylococcus aureus, methicillin-resistant Staphylococcus aureus, Pseudomonas aeruginosa, and Bacillus subtilis. The results obtained in this study could potentially benefit future research in nanomedical-driven fields.