Biocatalytic and biogenic pathways for sustainable nanoparticle synthesis: mechanisms, monitoring, and circular bioeconomy integration.

Due to the growing demand for eco-friendly nanomaterials, biocatalytic and biogenic nanoparticle production methods have developed as greener alternatives to traditional physicochemical approaches. Traditional methods involve hazardous byproducts, large energy inputs, and toxic chemicals, which pose concerns regarding biocompatibility, scalability, and environmental effect. Plants, bacteria, enzymes, and agricultural waste are all natural stabilizers, cappers, and reducers used in biogenic synthesis. Proteins, polysaccharides, oxidoreductases, extracellular polymeric substances, and phenolic chemicals are all important in the nucleation, growth, and stability of biogenic nanoparticles. This review investigates the intracellular, cell-surface, and extracellular mechanisms of biogenic nanoparticle production. It also examines advanced characterisation tools like as time-resolved techniques, FT-IR, Raman spectroscopy, TEM, SEM, XRD, and UV-Vis spectroscopy to get insights into kinetic and structure-function relationships. The use of agricultural and food processing wastes as feedstocks is being researched as part of waste valorisation and the circular bioeconomy, with an emphasis on environmental sustainability and resource efficiency. Scale-up concerns and industrial translation are also considered when critically reviewing bioprocess design factors such as reactor structure, medium optimisation, strain selection, and nanoparticle size and surface chemistry management. Techno-economic analysis, process analytical technology, quality by design, and life-cycle assessment are all discussed as methods for ensuring environmental viability, regulatory compliance, and reproducibility. Finally, transdisciplinary applications in environmental remediation, biomedicine, pharmaceuticals, and agriculture are discussed, as well as the challenges involved with commercialization and regulation. The combination of biocatalysis, nanotechnology, and circular bioeconomy principles opens up a revolutionary path to sustainable nanomanufacturing and next-generation functional nanomaterials.