Microbial silver nanoparticles: Synthesis, characterization and applications

Abstract

In recent times, the biological synthesis of silver nanoparticles (AgNPs) has become a viable alternative to conventional physical or chemical methods, since it is easy, fast and environmentally friendly. In addition, this synthesis carried out from plants or microorganisms, have been found to give nanoparticles colloidal stability, as well as to control their size and shape. Microbial-based synthesis may be advantageous due to the large number of metabolites produced, thus increasing productivity. These organisms are widely used as reducing and stabilizing agents, due to their tolerance to heavy metals and their ability to internalize and bioaccumulate metals. It also has advantages from the industrial point of view, such as the production of large amounts of proteins and extracellular enzymes, ease in handling biomass, good dispersion of AgNPs and easy handling in large-scale production. Microorganisms are the source of the stabilizing agent (capping) that constitutes the biogenic AgNPs. This capping agent provides stability and can also present biological activity, acting in synergy with the effect of the core of the AgNPs. For example, it has recently been shown that in addition to providing greater antimicrobial activity, this stabilizing agent would be responsible for less cytotoxicity and genotoxicity, a fundamental factor to consider for its use as a therapeutic agent in human and animal health. Several fungal AgNPs have shown broad antimicrobial activity against Gram-negative and Gram-positive bacteria and plant pathogenic fungi. Furthermore, the effectiveness of these microbial nanoparticles in the eradication of microbial biofilms was reported. Moreover, the antimicrobial potential of biogenic silver nanoparticles is very promising in the agri-food area, in food preservation or in the control of phytopathogens with a high impact in agriculture. The antimicrobial action mechanisms of biogenic nanoparticles are not completely elucidated and depend on their characteristics (shape, size, composition, surface charge). That is why there have been advances in recent years in studies of interactions of biogenic nanoparticles with microbial cells as well as their possible antimicrobial mechanisms of action. All these advances in the knowledge of the characteristics and biotechnological properties of microbial silver nanoparticles will encourage new challenges in the development of nanomaterials, in their production on a larger scale, as well as in their expanded use in the area of human and animal health, agriculture, food and materials.