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A novel biological method for the synthesis of silver nanoparticles using the fungus Verticillium is reported. Exposure of the fungal biomass to aqueous Ag + ions resulted in the intracellular reduction of the metal ions and formation of silver nanoparticles of dimensions 25 ± 12 nm. Electron microscopy analysis of thin sections of the fungal cells indicated that the silver particles were formed below the cell wall surface, possibly due to reduction of the metal ions by enzymes present in the cell wall membrane. The metal ions were not toxic to the fungal cells and the cells continued to multiply after biosynthesis of the silver nanoparticles.

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A green chemistry approach to nanoparticle synthesis is the exciting possibility opened up by the fungus Fusarium oxysporum. The fungus (shown in the flask on the left), when exposed to aqueous AuCl4− ions, reduces the metal ions; this leads to the extracellular formation of gold nanoparticles (shown in the flask on the right).

The biosynthesis of Q-state CdS nanoparticles by reaction of aqueous CdSO4 solution with the fungus, Fusarium oxysporum, is demonstrated. Nanoparticle formation proceeds by release of sulfate reductase enzymes by the fungus, conversion of sulfate ions to sulfide ions that subsequently react with aqueous Cd2+ ions to yield highly stable CdS nanoparticles. Elucidation of an enzymatic pathway using fungi opens up the exciting possibility of developing a rational, biosynthesis strategy for nanomaterials over a range of chemical compositions which is currently not possible.