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

Silver nanoparticles (AgNPs) were synthesized via a green approach using Mentha spicata (M. spicata) extract. The extract was prepared using three methods, namely Soxhlet extraction, maceration, and ultrasonic assisted extraction, and the yields were expressed as weight percentages relative to the dry plant materia. Soxhlet extraction yielded the highest extraction efficiency at 34.36%, whereas ultrasonic assisted extraction and maceration produced yields of 18.21% and 11.80%, respectively. Although ultrasonic-assisted extraction produced a lower extraction yield, it was selected as the optimal approach due to its shorter extraction time, reduced solvent consumption, and higher energy efficiency than the other methods. The antioxidant capacity of M. spicata extract was notably high, with a total polyphenol content of 106.22 mg gallic acid equivalents per gram of dry plant material and an IC₅₀ value of 34.02 μg/mL in the DPPH assay. Key parameters for AgNP synthesis were optimized, including pH 9, temperature of 60 °C, and extract concentration of 1.0 g/L. XRD confirmed the crystalline structure, FTIR identified functional groups, and SEM revealed an average particle size of approximately 58.41 nm. The synthesized AgNPs exhibited significant antibacterial activity against Staphylococcus aureus, Proteus mirabilis, and Salmonella typhimurium at the tested concentration of 5 mg/mL, highlighting the importance of optimizing extraction and synthesis conditions to enhance the bioactivity of nanoparticles.