Microbial-Based Green Synthesis of Silver Nanoparticles: A Comparative Review of Bacteria- and Fungi-Mediated Approaches

The growing demand for sustainable and eco-friendly technologies has driven the development of green and bio-based synthesis methods for metallic nanoparticles. Among these, the microbial synthesis of silver nanoparticles (AgNPs) has emerged as a promising alternative to conventional chemical methods, which often rely on hazardous reagents and harsh conditions. Bacteria and fungi are particularly attractive due to their ability to produce AgNPs with tunable size, shape, and surface properties through natural enzymatic and metabolic processes. This review provides a comparative analysis of bacterial and fungal synthesis routes, focusing on their distinct advantages, limitations, and optimal applications. Bacterial synthesis offers faster growth, simpler culture requirements, and greater potential for genetic manipulation, enabling precise control over nanoparticle (NP) characteristics. In contrast, fungal synthesis typically yields higher nanoparticle stability and is well suited for extracellular, scalable production. The review also summarizes key synthesis parameters (e.g., pH, temperature, reaction time), addresses reproducibility and scalability challenges, and highlights emerging research areas, including antibacterial bio-hybrid materials and bacterial-supported metallic catalysts. Overall, this comparative perspective provides a clear framework for selecting appropriate microbial systems for different technological applications and identifies future research directions to advance green nanotechnology.