Green Synthesis of Silver Nanoparticles from Mentha spicata L. Aqueous Extract and Evaluation of Its Antioxidant, Antibacterial and Anticancer Activities

Abstract

Mentha spicata L. (Lamiaceae) has been used in traditional medicine to cure indigestion, stomach aches, intestinal weakness, and diarrhea. This research was designed to synthesize silver nanoparticles from an aqueous extract of M. spicata and to investigate its antioxidant, antibacterial, and anticancer activities. The was extracted by maceration with water and silver nanoparticle MAgNPs were prepared using 5 mM of AgNO3 solution. The DPPH free radical and hydrogen peroxide scavenging assays were conducted to determine the antioxidant activity. The antibacterial activity was determined using the agar disk diffusion method on Staphylococcus aureus, Bacillus subtilis, Salmonella typhi, and Escherichia coli. Anticancer studies were carried out, to determine the cytotoxic and anti-proliferative effect of MAgNPs. The phytochemical screening of the extract revealed the presence of phenolic compounds (flavonoids and tannins). The aqueous extract and MAgNPs scavenged the DPPH free radical, with IC50 values of 12.62 µg/mL and 1.556ug/mL respectively, while the IC50 of the aqueous extract and MAgNPs against H2O2 were 1.695 mg/mL and 5.865 mg/mL. The bacterial strains were susceptible to the extract and MAgNPs with a zone of inhibition ranging between 4–11 mm. The zeta analysis of MAgNPs reveals a size of 70.08 nm and a potential of -13.17 mV. The SEM revealed spherical shape particles. The XRD showed the crystalline structure of MAgNPs. The FTIR revealed the N-H stretching frequency in the MAgNPs indicating the stretching of secondary amine. There was an in vitro cytotoxic effect on the viability of MDA MB 231 cancer cells with a significant difference among means (p < 0.05). The MTT Assay showed an anti-proliferative effect against the cells. The MAgNPs were found to be potent against MDA MB 231 breast cancer cells with IC50 values of 11.67 µg/mL and 31.57 µg/mL obtained after 24 hours and 48 hours respectively. Therefore, the ability of the extract to scavenge the free radicals and inhibit the growth of the bacteria may be due to its chemical constituents.