Background: Nowadays, biosynthesis of nanoparticles is considered because of its low energy requirements and risk. In present study, silver nanoparticles produced by two species of lichens “Usnea articulata” and “Ramalina sinensis”. Furthermore, the antibacterial effects of nanoparticles were studied.

Materials and Methods: To produce silver nanoparticles, lichens aqueous extract was placed in the vicinity of 1mmol of the silver nitrate solution. The production of nanoparticles was studied by spectroscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM). The antibacterial effect of the produced silver nanoparticles was investigated by agar well diffusion method against Escherichia coli، Pseudomonas aeruginosa، Bacillus subtilis, and Staphylococcus aureus.

Results: The biosynthesized nanoparticles by two types of lichens had a maximum absorption at the wavelengths of 450 and 480 nm. Also, the presence of silver nanoparticles was confirmed by XRD method. The size of silver nanoparticles produced by Usnea articulata was about 10 to 50 nm and the nanoparticles produced by Ramalina sinensis around was 50 to 80 nm. The antibacterial test of the nanoparticles showed a good inhibitory effect against all four bacteria.

Conclusion: Lichens can be a good choice to produce silver nanoparticles, due to the abundance, fast growth, and environmental sustainability. The results of present study showed that biosynthesized silver nanoparticles had an effective inhibitory activity against bacteria. Therefore, these nanoparticles can be used in various industries.