Green synthesis of silver nanoparticles derived from the secondary metabolites of Gliocladium flavum and the exploration of their antimicrobial potentials

In modern times, green nanotechnology has become a powerful tool in developing nanomaterials that are environmentally sustainable and have broad applications. Nanoparticles can be synthesized via biosynthesis using algae, bacteria, fungi, and plants. This is preferred because of its environmental friendliness, cost-effectiveness, biocompatibility, and its non-toxic approach to the synthesis of nanoparticles which is assisted by the compounds, metabolites, and enzymes naturally present in the organism. Therefore, this study investigated the potential of the entomopathogenic fungus (EPF) Gliocladium flavum to act as a reducing and capping agent for the extracellular green synthesis of silver nanoparticles (AgNPs) with antimicrobial properties. The cell-free extract-to-precursor ratios used were 1:9, 1:1, and 9:1 for three different concentrations of AgNO3 (1, 5, and 10 mM). The mycosynthesis was aided with constant stirring and heating at 40–80 °C for 1 h, and the color change of the reaction mixtures initially confirmed the successful synthesis. Furthermore, the mycosynthesized G. flavum-AgNPs (Gf-AgNPs) were characterized using Ultraviolet-Visible (UV-Vis) and Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy, and Dynamic Light Scattering (DLS). Results showed characteristic surface plasmon resonance (SPR) peaks in the wavelength region 380 to 450 nm. ATR-FTIR displayed the different functional groups that act as capping and reducing agents for the synthesis, while DLS studies indicated an average particle diameter of 161.7 nm, polydispersity index (PDI) of 0.658, and zeta potential of−25.5 mV, indicating moderately polydispersed but slightly larger stable nanoparticles. Gf-AgNPs were evaluated for their antimicrobial activities against gram-positive bacteria (Bacillus subtilis ATCC 11774 and Staphylococcus aureus ATCC 25923), gram-negative bacteria (Pseudomonas aeruginosa ATCC 27853 and Escherichia coli ATCC 25922), and fungi such as mold (Aspergillus niger ATCC 16888) and yeast (Candida albicans ATCC 10231). Prominent antimicrobial activities as indicated by the zone of inhibitions (ZOI) ranging from 2.2 ± 2.23 mm to 12.4 ± 0.09 mm were exhibited by the AgNPs across all tested microorganisms. Thus, this study provides a novel approach for the synthesis of nanoparticles with antimicrobial efficacy against medically important pathogens. G. flavum extracts enabled the eco-friendly mycosynthesis of stable silver nanoparticles (AgNPs) in aqueous medium. A novel synthesis approach integrating constant stirring and heating (40–80 °C) significantly enhanced AgNP production. Biosynthesized AgNPs showed broad-spectrum antimicrobial activity against tested strain.