Sustainable Biogenic Fabrication of SnO₂ Nanoparticles via Macrotyloma uniflorum Seed Extract: Structural Optimization and Enhanced Antioxidant and Antidiabetic Activity

• Eco-friendly SnO₂ nanoparticles synthesized using M. uniflorum seed extract. • Size-dependent absorption reveals tunable optical traits in SnO₂ nanoparticles. • XRD, XPS, and TEM confirm the nanoscale structure of synthesized SnO₂ particles. • SnO₂ nanoparticles display promising antioxidant and antidiabetic potential. • A low-cost, sustainable synthesis route with broad biomedical uses. Nanostructured tin oxide is valued for its large surface area and quantum effects, which give it physical and chemical properties very different from those found in bulk tin oxide. In this study, an environmentally sustainable and cost-effective green synthesis route, employing Macrotyloma uniflorum seed extract as a biogenic reducing and stabilizing agent in place of conventional chemical precursors, is adopted. This approach not only eliminates the use of toxic reagents but also introduces phytochemical-mediated surface functionalization, which influences nucleation, growth, and particle stability. The synthesis parameters were systematically optimized to yield nanoparticles with enhanced uniformity and crystallinity. Upon thermal treatment, the particle size increased progressively from ∼3.1 nm at 300°C (MS 43 ) to 11.0 nm at 600°C (MS 46 ) and 14.4 nm at 900°C (MS 49 ), demonstrating the strong influence of annealing on particle growth and crystallite coarsening, while the initial extract concentration governs size control in the as-synthesized nanoparticles. A size-dependent shift in the absorption edge was observed, reflecting the tunable optical properties imparted by the green synthesis route. Optical studies using the Kubelka–Munk approach indicated band gap values in the range of ∼3.5–4.0 eV. The present study highlights the role of green chemistry-derived approaches in enhancing the bio-efficacy of tin oxide (SnO₂) nanoparticles. Both as-synthesized and annealed SnO₂ nanoparticles exhibited pronounced antioxidant and antidiabetic activities, demonstrating the combined influence of surface-bound phytoconstituents and defect engineering. This work illustrates how a green chemistry approach not only ensures sustainability but also tailors the physicochemical and functional properties of SnO₂ for potential biomedical and nanotechnology applications.