Green Synthesis of Gold Nanoparticles using Melissa Officinalis L. Aqueous Extract: Optimization, Antioxidant Activity and In Vitro Cell Viability

Gold nanoparticles possess attractive properties that make them valuable in medicine. Recently, green synthesis of nanoparticles has been a target of research due to its simplicity, safety, eco-friendliness and cost-effectiveness. This study describes the green synthesis of gold nanoparticles via aqueous extract of Melissa officinalis L. (Mel). The various parameters affecting the synthesis of gold nanoparticles (pH, gold salt concentration, extract volume, temperature, and reaction time) were investigated and optimized. Ultraviolet–Visible spectrophotometry, Dynamic light scattering, Transmission electron microscopy, and Fourier-transform infrared spectroscopy were applied to characterize synthesized gold nanoparticles (GNP-Mel). The antioxidant activity of Mel extract and GNP-Mel was performed by 2,2-diphenyl-1-picrylhydrazyl free radical scavenging test. The effect of GNP-Mel on cell viability of H9C2 rat cardiomyocytes was evaluated using Alamar blue assay. The results indicated uniform spherical-shaped gold nanoparticles with an average particle size of 8 nm and a zeta potential value of -31.7 mV, which demonstrates the high stability of GNP-Mel. The Mel extract and GNP-Mel showed the highest antioxidant activity with percentages of 77.69 ± 1.18% and 59.64 ± 1.29% at a maximum concentration (of 100 μg/ml), respectively, which can be compared with Vitamin C (89.34 ± 1.34%). Moreover, the result of Alamar blue assay represented a higher than 80% cell viability in the presence of 20, and 50 μg/ml of GNP-Mel and likewise, a higher than 50% cell viability in the presence of 100 and 170 μg/ml of GNP-Mel. Overall, the findings show that the green synthesized gold nanoparticles are appropriate candidates for biomedical applications.