Biological synthesis of α-Ag₂S composite nanoparticles using the fungus Humicola sp. and its biomedical applications

Synthesis of α-Ag₂S (silver sulfide) is a highly challenging task, usually attempted using synthetic, hazardous chemical processes. This report puts efforts to exploring microbial-based eco-friendly alternatives. A facile, one-pot biological method for the synthesis of α-Ag₂S composite nanoparticles (NPs) in an aqueous medium at ambient conditions was established. As prepared α-Ag₂S composite NPs were efficiently produced from precursors silver nitrate and sodium sulfite. The extracellular biomolecules produced by Humicola sp. reduced the precursor solution and at the same time it capped the formed Ag₂S NPs. The characterization performed by different techniques revealed excellent optical, morphological, and structural properties (size, shape distribution, and crystallinity) of the α-Ag₂S NPs. The change in color from colorless to dark brown indicated the formation of α-Ag₂S, which was further confirmed by fluorescence and UV–Visible spectroscopy, showing a sharp peak at 410 nm. Morphological analysis of α-Ag₂S NPs confirmed the spherical shape, and narrow size distribution. α-Ag₂S NPs were found to be potent in antimicrobial applications owing to their high dispersibility in water and capping by extracellular biomolecules secreted by Humicola sp. The anti-cancer activity for α-Ag₂S performed using human breast cancer cell line (ZR-75-1) and human Burkitt's lymphoma cancer (Daudi). The biocompatibility test was performed using human peripheral blood mononuclear cells (PBMCs) for α-Ag₂S NPs. The anti-leishmania activity was also determined for αAg₂S NPs in-vitro using the standard anti-promastigote protocol (Leishmania donovani promastigotes). This extracellular system is an economically and environmentally benign route for the biosynthesis of α-Ag₂S NPs having desired surface, structure and biomedical properties.