Green Sustainable Synthesis of Silver Nanoparticles from Extracts of Garden Spearmint Mentha spicata for Antibiotic and Antioxidant Activities

Abstract

Silver nanoparticles (AgNPs) were synthesized using a green route with Mentha spicata (M. spicata) extract. The extract was prepared through three methods (Soxhlet, maceration, and ultrasonic-assisted extraction) and the yields were compared as weight percentages of dry plant material. Soxhlet extraction gave the highest yield of 34.36% while ultrasonic-assisted extraction and maceration provided yields of 18.21% and 11.80%, respectively. Although ultrasonic-assisted extraction method had lower yield, it was selected as an optimal one due to shorter extraction time, less solvent consumption, and high energy efficiency among other methods. The antioxidant capacity of M. spicata extract was very high with total polyphenol content at 106.22 mg gallic acid equivalents per gram of dry plant material and IC₅₀ at 34.02 μg/mL in the DPPH assay; key synthesis parameters for AgNPs were optimized pH (9), temperature (60 °C), and extract concentration (1.0 g/L). Characterization by X-ray diffraction, Fourier-transform infrared spectroscopy, and scanning electron microscopy confirmed the crystalline structure, functional groups, and average particle size of about 58.41 nm; these synthesized AgNPs showed significant antibacterial activity against Staphylococcus aureus, Proteus mirabilis, and Salmonella typhimurium at a concentration of 5 mg/mL to emphasize optimizing extraction and synthesis conditions for better bioactivity of nanoparticles.