International Journal of Scientific Research and Engineering Development

Bio-inspired synthesis of nanoparticles has become one of the most promising branches of green chemistry due to its low environmental impact, mild reaction conditions, and avoidance of toxic chemical reagents. Plants, microorganisms, enzymes, proteins, biopolymers, and other biomolecules possess intrinsic reducing and capping capacities, enabling the formation of metal and metal-oxide nanoparticles under ambient conditions. These green routes align strongly with the 12 principles of green chemistry and circumvent the ecological burden associated with conventional high-energy physicochemical methods. Recent studies have documented an expansion in the diversity of biological sources and mechanisms, with plant phytochemicals, microbial enzymes, and biomacromolecules offering precise control over nanoparticle nucleation, growth, surface functionalization, and stability. Despite remarkable advancements, key challenges remain, particularly in mechanistic understanding, extract variability, reproducibility, toxicity evaluation, scale-up, and regulatory compliance. This review presents an expanded, critical discussion of bio-derived nanoparticle synthesis, integrating advancements in plant-, microbe-, enzyme- and polymer-mediated strategies, incorporating recent mechanistic insights, technological developments, nanotoxicological evidence, engineering strategies for scale-up, and emerging hybrid biosynthetic approaches. Four comprehensive tables summarizing mechanisms, biological routes, applications, and characterization challenges are provided to enhance clarity. The review concludes with future perspectives emphasizing synthetic biology, omics-based profiling, in situ spectroscopic monitoring, continuous-flow microreactor systems, and AI-assisted optimization as essential tools to advance green nanotechnology toward industrial realization.