Green synthesis and Antibacterial Effect of Gold Nanoparticles using Mentha piperita L. Extract

Nanoparticles are used as a pharmaceutical tool for infections against microbes and in the near future, there is an urgent need to replace antibiotics with new substances with antibacterial properties. One of the most efficient methods of nanoparticle synthesis is the method of green synthesis of nanoparticles by plants. In this study, an environmentally friendly extracellular biosynthesis method, namely reducing agents of Mentha piperita L. extract, was used to produce gold nanoparticles. The gold nanoparticles were characterized by color changes, the XRD method and the UV-visible spectroscopy and the antibacterial activity of nanoparticles against four species of bacteria (Staphylococcus aureus, Escherichia coli, Salmonella typhimurium, and Bacillus cereus) investigated through bacteria disc fusion assays. Results showed that due to the reduction of gold ions and the production of nanoparticles, the color of the samples changed from yellow to brown, which indicates the production of a colloidal suspension of gold nanoparticles. The gold nanoparticles have the maximum absorbance at 550 nm, spherical shape and their average size was 2-10 nm. Further investigation revealed that synthesized nanoparticles have relatively antibacterial activity on Escherichia coli, Salmonella typhimurium but have no effect on Bacillus cereus and Staphylococcus aureus. In general, based on the observations of this study, it can be concluded that the aqueous extract of Mentha piperita L. due to its secondary components and antioxidant activity, has high potential in the reduction of gold metal ions as well as synthesis and stabilization of gold nanoparticles. Also, the synthesized gold nanoparticles show relatively good antibacterial activity against some bacteria.