Extracellular Biosynthesis of Gold and Silver Nanoparticles using Fungal Extracts

Nanoscience has opened new vistas to manage phytopathogens, improve crop productivity by the development of new varieties, and control infectious diseases in humans. Silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs) are highly acclaimed for their wide potential application in various fields. Chemical and physical methods of synthesis of AgNPs and AuNPs are widely used; however, such methods possess numerous setbacks, such as the production of toxic residues and indispensable need for high energy. Biosynthesis of nanoparticles is a cost-effective and environmentally friendly method. A plethora of species of plant, bacteria, fungi, etc. is available with potential biosynthesis ability. Fungi are a highly preferred organism owing to the ability to secrete a large number of extracellular enzymes, metal toxicity tolerance and bioaccumulation ability, and ease of handling of its biomass. Extracellular enzymes act both as reducing as well as capping agents. Two different methods are used by fungi for synthesis viz., intercellular and extracellular synthesis. Extracellular synthesis is preferred over intercellular as it bypasses several down streaming processes. During the reduction process, the metal ions (Ag2+ and Au3+) are converted to an elemental state (Ag0 and Au0 ) which is in the nano range. Due to their large surface-to-volume ratio and other properties, they become very effective against other pathogens. There is an excellent prospect of the use of nanoparticles in the field of agriculture and health and nanoparticles synthesized using a biological method involving fungi could be a boon. 

Keywords: Bacteria, Biosynthesis, Extracellular synthesis, Fungi, Nanoparticles, Nanoscience, Phytopathogens.