Today, nano metal particles have drawn the attention of scientists because of their extensive application to new technologies in chemistry, electronics, medicine, and biotechnology. Beside many physical and chemical methods which have been developed for preparing metal nanoparticles, nanobiotechnology also serves as an important method in the development of clean, nontoxic, and environmentally friendly procedures for the synthesis and assembly of metal nanoparticles. To be utilized in different scientific fields, biological synthesis still requires the optimization of reaction conditions, and an understanding of the biochemical and molecular mechanisms of the reaction for obtaining better chemical composition, shape, size, and monodispersity. By noticing the potential of the natural world to produce bio-nanomaterials under normal conditions, we are trying to explain simple practical methods that can be used for bacterial synthesis of metal or metalloid nanoparticles. In conclusion, the filamentous fungus has shown potential for extracellular synthesis of fairly monodispersed, silver nanoparticles in the range of 5–20 nm. The kinetics of silver nanoparticles synthesis using the cell filtrate indicates that the synthesis of nanoparticles would be suitable for developing a biological process. Furthermore, the extracellular synthesis would make the process simpler and easier for downstream processing. In future, it would be important to understand the biochemical and molecular mechanism of the synthesis of the nanoparticles by the cell filtrate in order to achieve better control over size and polydispersity of the nanoparticles.
