Microbial synthesis of metal and semiconductor nanoparticles

Overall, the literature suggests that a case for the serious investigation of microorganisms has been made as a possible alternative to the more popular physical and chemical methods that are currently prevalent. Biological methods are simple, practical, and unexpensive for producing novel metallic nanoparticles possessing unique chemical and physical properties. However, number of issues need to be address from the nanotechnology and microbiology points of view before such biosynthetic procedures can compete with the traditional protocols. The surface chemistry of biogenic nanoparticles should be properly recognized (i.e. nature of capping surfactants / peptides / proteins). The elucidation of biochemical pathways leading to metal ion reduction in the different classes of microbes is necessary to develop a rational microbial nanoparticle synthesis procedure. Genetic engineering techniques can potentially be used to improve the particle properties and to control their composition. At present, microbial methods in the synthesis of nanomaterials of varying composition are extreme limited and confined to some metals, semiconductors and very few oxides. Most importantly, the monodispersity of the nanoparticles produced either intra- or extracellularly by tested microorganisms is not very high and far inferior to that obtained through conventional chemical methods. Significant improvement in the monodispersity has been achieved using extremophilic microorganisms. (author)