Current overview of the mechanistic pathways and influence of physicochemical parameters on the microbial synthesis and applications of metallic nanoparticles

Microbe-assisted synthesis of metallic nanoparticles (NPs) has carved a niche among different NP generation methods owing to its simplicity, non-toxicity, low energy requirements, and potential scalability. Microorganisms have ability to produce NPs both intracellularly and extracellularly due to the presence of enzymes, proteins, and other biomolecules that can act as reducing and capping agents. However, a complete mechanistic understanding of this biosynthesis remains elusive. Biosynthesis is influenced by a myriad of factors, such as pH, temperature, reactant concentrations, reaction time, and light. The physicochemical factors associated with the synthesis process affect the morphological, biological, and catalytic properties of the NPs produced. This review focuses on the current paradigm and gaps in our understanding of microbial production pathways and the effects of physicochemical factors on the synthesis and application of various types of metallic NPs. The surveyed literature clearly elucidated the effect of these factors on the size, shape, dispersity, surface properties, and the reaction kinetics. The variations in morphological and surface properties were found to affect the performance of NPs in different applications such as catalysis, antimicrobial, and anticancer activities. Understanding the mechanistic pathways and the influence of physicochemical factors on synthesis can be potentially beneficial for the production of NPs with controlled shapes and sizes, tailored for specific applications.