Antifungal activity of different size controlled stable silver nanoparticles biosynthesized by the endophytic fungus Aspergillus terreus

Silver nanoparticles (AgNPs) synthesized by using the aqueous extract of the endophytic fungus Aspergillus terreus F37 (KX024595) as reducing agent is reported here. The reaction medium employed in the synthesis process was optimized under a narrow range of pH and temperature to attain better yield, controlled size, and more stable of AgNPs. Further, the microbially synthesized AgNPs were studied through UV-vis spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), and Fourier transform infrared (FT-IR) spectroscopy analyses. The obtained results indicated the formation of high crystalline spherical AgNPs with an average diameter of 45.2±0.5 nm at room temperature (22 ºC). Quantitative analyses indicated that reduction of the Ag+ precursor was promoted at elevated pH due to increased activity of biomolecules in the fungal extract. As a result, the size of the AgNPs decreased with increased pH of the reactions. The optimum conditions for maximum production of small control sized AgNPs (12± 0.5 nm) were pH (10) and temperature (100 ºC). The outcomes of the antifungal activity of different controlled sized AgNPs showed their efficiently to inhibit the mycelial growth of the pathogenic fungus Alternaria solani, the causal agent of tomato early blight disease and reduced their viability in a pH and temperature dependent manner. These findings revealed that the fine tuning of the reaction synthesis parameters, will increase the chance to obtain desired well shaped and small sized AgNPs with potent antifungal activities, may have important applications as new bio-fungicides in controlling various plant diseases caused by fungi