Effect of Different Ratios of Mentha spicata Aqueous Solution Based on a Biosolvent on the Synthesis of AgNPs for Inhibiting Bacteria

Abstract

Our work was devoted to studying the effect of different concentrations of Mentha spicata aqueous extract on the green synthesis of silver nanoparticles (AgNPs) in order to obtain the most effective of these concentrations for bacteria inhibitory activity. Different concentrations of the aqueous M. spicata extract (0.25, 0.50, 0.75, and 1.00 mM) were used as biological solvent to synthesize AgNPs by means of the reduction method. The crystal structure and morphology of the NPs were characterized UV–vis spectra, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The inhibition effect of AgNPs on Escherichia coli was studied to determine the minimum inhibitory concentration (MIC). The dark yellow color of the M. spicata extract aqueous solution indicates the successful synthesis of the AgNPs. UV spectra of the NPs show a gradual increase in absorption with increasing concentration of aqueous M. spicata extract solution from 0.25 to 1.00 mM, accompanied by a shift in the wavelength from 455 to 479 nm along with a change in the nanoparticle size from 31 to 9 nm. The tests also showed a high activity of the particles against bacteria (E. coli) ranging between 15.6 and 62.5 µg/ml. From the AgNPs, it was confirmed that aqueous M. spicata extract is an effective biosolvent for the synthesis of different sizes of AgNPs according to the solvent concentration. The AgNPs also proved effectual for the killing of bacteria.