Significance of secondary metabolites for synthesis of metal and metal oxide nanoparticles and their applications.

Secondary metabolites, produced by plants, fungi, and microorganisms, are a diverse group of bioactive compounds that play crucial roles in ecological interactions and defense mechanisms. In recent years, these metabolites have garnered significant attention as natural reducing, stabilizing, and capping agents in the green synthesis of metal and metal oxide nanoparticles (NPs). Phytochemicals such as flavonoids, alkaloids, terpenoids, saponins, tannins, and phenolic acids possess functional groups capable of mediating the reduction of metal ions to nanoscale forms while providing stability against aggregation. This eco-friendly synthesis approach offers several advantages over conventional physical and chemical methods, including reduced toxicity, lower energy requirements, and cost-effectiveness. The nature and concentration of secondary metabolites directly influence nanoparticle size, morphology, and functional properties, which in turn determine their potential applications. Metal and metal oxide nanoparticles synthesized using secondary metabolites have demonstrated broad-spectrum applications in antimicrobial, antioxidant, anticancer, and anti-inflammatory therapies, as well as in environmental remediation, biosensing, and catalysis, their biocompatibility and stability make them promising candidates for use in biomedical devices and agricultural formulations, the biochemical mechanisms by which secondary metabolites mediate nanoparticle synthesis, the factors influencing synthesis efficiency, and the diverse applications of such biologically derived nanomaterials. Emphasis is placed on the sustainable potential of leveraging plant- and microbe-derived metabolites for scalable nanoparticle production to meet global needs in medicine, agriculture, and environmental management.