Fig. 3.

Schematic representation of extracellular synthesis mechanisms of ZnO NPs. The extracellular mechanisms involve enzyme-mediated synthesis such as nitrate reductase enzyme, which is secreted in the growth medium, to reduce the metal ions to their respective metal atoms and lead to nucleation and growth of NPs. The extracellular protein secreted by the microbes acts as a capping agent for NPs stabilization. The formation of white precipitation in the medium shows the production of NPs