Green silver nanoparticles from novel Brassicaceae cultivars with enhanced antimicrobial potential than earlier reported Brassicaceae members

Abstract

In the present study, we report perhaps for the first time the use of novel varieties of Brassica oleracea var. botrytis and Raphanus sativus as potential bioreductant, to synthesize highly stable silver nanoparticles (AgNPs, no aggregation observed for six months), which is a significant finding as plant extract-directed AgNPs are intrinsically unstable and tend to aggregate. The reduction of Ag⁺ to Ag⁰ nanostructures was confirmed using UVVis spectroscopy showing SPR spectra at 400-435 nm. Nanosight and transmission electron microscope (TEM) analysis showed monodisperse spherical AgNPs (4-18 nm). Fourier transform infrared spectroscopy (FTIR) analysis revealed that the polyphenolics and other secondary metabolites including glucosinolates in the aqueous extracts may act as reducing/capping agent for the nanoparticle synthesis. X-ray diffraction (XRD) confirmed the face centered cubic crystalline (fcc) structure of AgNPs. Controlled synthesis of AgNPs was achieved by varying experimental parameters (AgNO₃ concentration, extract volume, pH and temperature). These AgNPs exhibited strong antibacterial activity at significantly lower concentration (5 ppm) against both Gram negative (Escherichia coli, Myroides, Psuedomonas aeruginosa) and Gram positive (Kocuria and Promicromonospora) bacteria. In the present study, the green AgNPs showed (10-30%) better antimicrobial efficacy than chemical AgNPs and AgNPs from other Brassicaceae members. These green AgNPs may have promising application in nano-drug formulation to combat bacterial infections, in future.

Keywords: Antimicrobial activity; Brassicaceae; Cauliflower; Colored radish varieties; Green synthesis; Silver nanoparticles.