Microbial routes for metal-based nanoparticle synthesis: from mechanisms to functional applications

Microbial-mediated synthesis is an alternative approach to producing metal-based nanoparticles (MBNPs) using bacteria, fungi, and algae under relatively mild conditions compared with conventional physicochemical methods. Although the mechanism of MBNP formation is not fully understood, it is difficult to replicate and control nanoparticle properties. The review presents the key microbial pathways for MBNP synthesis, focusing on metal transformation and the formation and stabilization of nanoparticles. The roles of microbial species, biomolecules, precursor concentration, pH, temperature, and other synthesis parameters in controlling the formation of nanoparticles and their physicochemical properties were discussed, along with the optimization of the synthesis and process control. The obtained MBNPs and their use for antimicrobial applications, photocatalysis, and electrochemical sensing are also discussed. However, the use of MBNPs in electrochemical sensing, which can rapidly, sensitively, and cost-effectively detect environmental and biomedical analytes in a portable manner, is comparatively limited. Other issues of reproducibility, scale-up, purification, toxicity, environmental safety, and standardization are also covered; biofouling, real-matrix validation, long-term stability, and consistent analytical performance are still key points in the field of sensing applications. Mechanistic understanding, combined with systematic synthesis optimization, is of critical importance to achieve greater control over microbial MBNPs and the development of functional applications.