Background: Today, antibiotic resistance against bacteria causing infection is very common and biological production of nanoparticles is a suitable alternative. In the present study, the synthesis of silver nanoparticle of Hypericum perforatum plant and its antioxidant and antibacterial properties were investigated in comparison with antibiotic gentamicin.

Materials and methods: After collecting plant and preparing the aqueous extract, 1 mM silver nitrate was added for nanoparticle synthesis. The effect of pH parameters and silver nitrate concentration for the optimization of green nanoparticle was evaluated by spectrophotometry and SEM. Antioxidant properties were investigated by DPPH and ABTS free radical methods. Finally, the antibacterial properties of the above nanoparticle were determined by diffusion method in agar and minimum growth inhibitory concentration (MIC) and minimum bactericidal concentration (MBC).

Results: Silver nanoparticles from Hypericum perforatum extract showed highest absorption at 430 nm. Silver salt concentration and alkaline pH had an effect on its quantity. It is worth mentioning that resulting nanoparticle has antioxidant properties so that depending on concentration it has an inhibitory effect on free radicals with ABTS and DPPH methods; in these two methods by increasing concentration from 40 mg/ml to 250 mg/ml, amount of free radical inhibition increases and value of IC50 at  concentration of 40 mg/ml with ABTS and DPPH methods is 34.7±0.27 and 47.4±0.59, respectively The examination of results of antibacterial properties, shown that synthesized silver nanoparticles had the most antibacterial activity against standard strains of Listeria monocytogenes, Escherichia coli, Staphylococcus aureus and Salmonella enterica, respectively.

Conclusion: Hypericum perforatum extract is able to regenerate Ag+ ion and silver nanoparticles.Super nanoparticle has acceptable antioxidant and antimicrobial power.