<i>Aspergillus niger</i>-mediated Ag, Au, and Ag-Au nanoparticles, their antimicrobial activities and remediation properties

The increasing demand for environmentally sustainable nanotechnology has driven the adoption of biological systems as viable alternatives for nanoparticle synthesis. In this study, the filamentous fungus Aspergillus niger, obtained from a gas flaring region in Ologbo, Benin City, was utilized for the eco-friendly synthesis of silver (Ag), gold (Au), and silver-gold (Ag-Au) bimetallic nanoparticles (NPs). The organism’s natural resilience to harsh environmental conditions suggests potential suitability for stress-resistant NPs biosynthesis. The fungal strain was grown on potato dextrose agar under standard laboratory conditions, and its molecular identity was confirmed through an internal transcribed spacer (ITS) region sequencing. Nanoparticles synthesized from fungal biomass were characterized using UV–Vis, XRD, FTIR SEM and TEM confirming their formation, crystal structure, functional group interactions, surface morphology and particle size distribution. The antimicrobial properties of the nanoparticles were tested against clinical isolates of Staphylococcus sp., Klebsiella sp., Bacillus sp., and E. coli. The Ag and Au NPs showed strong activity against Staphylococcus sp. with inhibition zones of 13 mm and 10 mm, while Ag-Au NPs showed a minimal antibacterial effect. Ag-Au NPs showed the most effective oil degradation potential, forming clearance zones of 17 mm on MSM agar and 20 mm on Winogradsky agar, outperforming Ag NPs, which showed only 9 mm. These results highlight fungal-based NP synthesis as a sustainable method with potential for antimicrobial and environmental applications. The enhanced oil-remediation ability of Ag-Au NPs suggests their usefulness in oil spill response. Further studies will elucidate the mechanistic pathways behind their antimicrobial and clean-up effects. The study provides the first attempt to use A niger isolated from a gas flaring site to synthesize Ag, Au, and Ag-Au NPs and exploring their potential for oil remediation in contaminated soil.