Comparative green synthesis of zinc oxide nanoparticles using millet extracts and their physicochemical characterization and in vitro antidiabetic activity

Zinc plays an essential role in glucose metabolism, insulin storage, and antioxidant defense, and its deficiency has been linked to impaired pancreatic β-cell function and increased oxidative stress. In this study, zinc oxide nanoparticles (ZnO NPs) were synthesized through a green, plant-mediated approach using aqueous extracts of three commonly consumed millets (Eleusine coracana (finger millet), Pennisetum glaucum (pearl millet), and Panicum sumatrense (little millet)). The millet extracts acted as natural reducing agents during nanoparticle formation, leading to the production of crystalline ZnO nanoparticles under alkaline conditions.The synthesized ZnO NPs were characterized using UV-visible spectroscopy, Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM/TEM), dynamic light scattering (DLS), and zeta potential analysis to confirm their phase purity, morphology, crystallinity, and colloidal stability. The nanoparticles exhibited a hexagonal wurtzite ZnO structure with crystallite sizes in the nanometer range, while the hydrodynamic sizes were larger due to surface hydration and aggregation effects.In vitro biological evaluation showed that millet-derived ZnO NPs exhibited dose-dependent inhibition of carbohydrate-digesting enzymes (α-amylase and α-glucosidase) along with moderate inhibition of dipeptidyl peptidase-IV (DPP-IV). Cellular studies using INS-1 pancreatic β-cells and 3T3-L1 adipocytes demonstrated enhanced glucose-stimulated insulin secretion and increased glucose uptake at non-cytotoxic concentrations. In addition, the nanoparticles showed antioxidant activity, as indicated by reduced intracellular reactive oxygen species (ROS) levels and increased activities of endogenous antioxidant enzymes.Overall, this study demonstrates that millet extracts can be effectively used for the green synthesis of ZnO nanoparticles, producing nanomaterials with promising in vitro antidiabetic and antioxidant properties. The comparative evaluation across different millets also provides useful insight into how phytochemical composition influences nanoparticle characteristics and biological performance.