Phytofabrication of gold and bimetallic gold-silver nanoparticles using aqueous extract of wheatgrass (Triticum aestivum L.), their characterization and assessment of antibacterial potential

In the present study, gold (AuNPs) and gold-silver bimetallic nanoparticles (Au-Ag BMNPs) were fabricated by using aqueous leaf extract of Triticum aestivum L. a crop plant, and their bactericidal potency was checked against selected pathogenic bacterial strains. The phytofabricated AuNPs and BMNPs were analyzed for their physical attributes using UV-Visible and Fourier transformed infrared spectroscopy (FTIR), Dynamic light scattering (DLS), High-resolution transmission electron microscopy (HRTEM), and Energy-dispersive X-ray spectroscopy (EDX). Bactericidal efficiency of synthesized NPs was evaluated using agar-well diffusion and XTT (2,3-Bis-(2-Methoxy-4-Nitro-5-Sulfophenyl)-2H-Tetrazolium-5-Carboxanilide)-colorime tric assays against Klebsiella pneumoniae, Salmonella typhimurium, Enterobacter aerogenes, Escherichia coli, Micrococcus luteus, Staphylococcus aureus, Streptococcus mutans and Staphylococcus epidermidis. HRTEM analysis revealed that both kinds of nanoparticles (NPs) were highly crystalline in nature and of spherical to oval-shaped. AuNPs size was found in the range of 5-40 nm, whereas BMNPs showed their size in the range of 5-30 nm. HRTEM results were corroborated by DLS results which revealed the average hydrodynamic diameter of AuNPs and BMNPs in the range of 29.08 and 26.56 nm respectively. UV-visible spectroscopy showed high-intensity single spectral peaks at 540 and 480 nm for AuNPs and BMNPs respectively. FTIR analysis demonstrated that protein, flavanones, hydroxyl, carboxylate groups and reducing sugars were responsible for reducing and capping of both NPs. K. pneumonia and S. typhimurium were found to be the most sensitive bacteria towards BMNPs-mediated (MIC: 400 mu g/ml) and AuNP-smediated toxicity (MIC: 800 mu g/ml). It was observed that BMNPs generally possessed more powerful bactericidal effect against all bacterial strains in comparison to AuNPs. Minimum inhibitory concentration (MIC) and Minimum bactericidal concentration (MBC) values were observed in the concentration range of 400 mu g/ml-1.5 mg /ml for different bacterial strains. Furthermore, it was demonstrated that phytosynthesized AuNPs have their own bactericidal effect, but at higher concentrations (>100 mu g/ml) and bactericidal effect of BMNPs was due to the synergistic effect of both Ag and Au ions, which was also observed to be dose-dependent.