Gold Nanoparticles from Chenopodium botrys and Chenopodium ambrosioides as Bioreductants: In Vitro Antioxidant, Antibacterial, and an Eco-friendly Catalytic Potential in Dyes Degradation

The present study focuses on synthesis of gold nanoparticles, quantification of total phenolic content (TPC), and total flavonoids content (TPC), antimicrobial potential, and catalytic activity of Chenopodium botrys and Chenopodium ambrosioides. Gold nanoparticles (AuNPs) due to unique surface texture are considered as promising alternative to synthetic antimicrobial and catalytic agents. TPC quantification revealed that ethanol and methanol extracts of C. botrys are rich with TPC (263.9 and 261.6 mg gallic acid equivalent per gram, mg GAE/g) whereas for C. ambrosioides, ethyl acetate extract exhibited higher content of TPC (273.2 mg GAE/g). Regarding TFC, ethyl acetate extracts of both species exhibited significant content (201.4 mg quercetin equivalent (QE)/g for C. botrys and 223.5 mg (QE)/g for C. ambrosioides). AuNPs synthesized with aqueous and ethanol extracts were respectively optimal in the concentration of 1:5 and 1:10 (extract:salt solution) under sunlight. The extracts and synthesized AuNPs were potential DPPH inhibitors with IC₅₀ values of 0.610–0.250 mg/mL. Moreover, the AuNPs significantly inhibited the microbial strains including S. aureus, E. coli, Candida albicans, and Aspergillus flavus with inhibition zones of 8.0–20.0 mm. In catalytic degradation of synthetic dyes (Congo red, methylene blue, methyl orange, Rhodamine B) and nitrophenols (ortho- and para-nitrophenols) in model water, AuNPs exhibited potential catalytic properties in the tested dyes and nitrophenols degradation (60–90%). From the results, it can be concluded that the species in question have promising therapeutic properties, and offers a safe, simple and cost-effective approach to wastewater treatment.