Green Synthesis of Gold and Silver Nanoparticles Using Invasive Alien Plant Parthenium hysterophorus and Their Antimicrobial and Antioxidant Activities

Abstract

Due to the high energy demands and environmental hazards of physical and chemical methods, it is now essential to produce nanoparticles using plant sources as reducing and stabilizing agents. In this study, silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs) were biosynthesized using an aqueous extract of Parthenium hysterophorus aerials as a reducing and stabilizing agent. The synthesized nanoparticles were characterized using UV–Vis spectroscopy, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, dynamic light scattering (DLS), and transmission electron Microscopy (TEM). UV–Vis spectroscopy indicates that the peaks of AgNPs and AuNPs are at 422 and 538 nm, respectively. The results of the DLS analysis showed that both Au and AgNPs are monodispersed and stable and have mean hydrodynamic sizes of 53.55 nm and 68.12 nm, respectively. According to an XRD analysis, the generated AgNPs and AuNPs are face-centered cubic crystals with average crystalline diameters of 33.4 nm and 30.5 nm, respectively. TEM image depicted that the synthesized NPs mainly have spherical shapes with particle size in the range of 3.41–14.5 nm for AuNPs and 5.57–26.3 nm for AgNPs. These biologically produced AuNPs and AgNPs were investigated for their antibacterial, antifungal, and antioxidant effects. Both AuNPs and AgNPs were found to strongly influence the growth of bacterial pathogens, with a maximum zone of 22.3 and 19.7 mm in Escherichia coli and a minimum zone of 11.7 and 10.3 mm in Salmonella enterica, respectively. The synthesized AuNPs and AgNPs reduce the numbers of viable fungi by 51.06% and 47.87%, respectively. The DPPH (2,2-diphenyl-1-picrylhydrazyl) assay revealed that the synthesized AuNPs and AgNPs have significant radical scavenging ability with 88.75% and 86.25% inhibition and 33.62 μg/mL and 42.86 μg/mL of IC50, respectively. Therefore, an aqueous extract of aerial parts of P. hysterophorus can be a suitable precursor for synthesizing AuNPs and AgNPs, with numerous applications. Due to their smaller size, AuNPs have better antimicrobial and antioxidant activities than AgNPs. This study supports the conservation by a utilization strategy of invasive alien plant species control and management (such as P. hysterophorus) for biodiversity conservation and environmental sustainability.