Silver nanoparticles biosynthesis using an airborne fungal isolate, Aspergillus flavus: optimization, characterization and antibacterial activity

Nanoscience is one of the most important branches of modern science, which deals with the knowledge, structure, and properties of nanoparticles. This study aimed to investigate the ability of an airborne fungus (Aspergillus flavus) to synthesize silver nanoparticles (AgNPs) and to test the antibacterial activity of the synthesized AgNPs.

The confirmation of AgNPs synthesis and the characterization of their properties were done using UV-Vis spectrophotometer, Zeta potential, Zeta sizer, FT-IR, and XRD analyses. The antibacterial activity was determined using broth microdilution method.

The findings showed that the average diameter of the resultant AgNPs was 474.2 nm with a PDI value of 0.27, and the zeta potential was -33.8 mV. Transmission electron microscopy (TEM) revealed that the AgNPs were regular and spherical in shape. TEM micrographs demonstrated that the AgNPs were smaller than those that were observed by DLS examination because the drying process resulted in particle shrinkage. The average size of AgNPs were less than 35 nm. The AgNPs exhibited a remarkable antibacterial activity against K. pneumoniae, E. coli, E. cloacae, S. aureus, S. epidermidis, and Shigella sp., and the MIC values ranged from 25 to 100 µg/mL. However, an exception was P. aeruginosa in which its MIC was >125 µg/mL.

The results suggest that, the biosynthesized AgNPs by A. flavus could be utilized as a source of potent antibacterial agents in medicine and biotechnological applications.