Sinapic acid-mediated green synthesis of silver nanoparticles: characterization, antioxidant capacity and antidiabetic enzyme inhibition

Green synthesis using chemically defined natural phenolic compounds offers a reproducible route to biofunctional nanomaterials. Here, sinapic acid-mediated silver nanoparticles (Sin-AgNPs) were prepared and evaluated for physicochemical characteristics, antioxidant capacity, and inhibition of carbohydrate-hydrolyzing enzymes. Condition screening selected pH 10, 50 °C, a 1:1 sinapic acid/silver nitrate volume ratio, and 8 mM silver nitrate. Ultraviolet–visible spectroscopy showed a surface plasmon resonance band at 400–450 nm. Scanning electron microscopy indicated predominantly spherical particles with dry diameters of approximately 31–96 nm, whereas dynamic light scattering gave a Z-average hydrodynamic diameter of approximately 96–97 nm. The zeta potential was −30.9 mV. Fourier transform infrared spectroscopy detected oxygen-containing bands consistent with sinapic acid-derived species associated with the recovered material, although these data alone do not prove a capping mechanism. In cell-free assays, Sin-AgNPs inhibited α-amylase and α-glucosidase, with IC50 values of 2.01 ± 0.17 and 5.89 ± 0.43 µg/mL, respectively. Under the same assay conditions, acarbose gave IC50 values of 18.55 ± 1.40 and 253.40 ± 5.14 µg/mL, respectively. Sin-AgNPs also produced measurable responses in 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), and ferrous-ion-chelation assays. Because residual free sinapic acid was not quantified, silver nitrate and free sinapic acid were not tested as direct controls, and cytotoxicity, long-term stability, and in vivo efficacy were not evaluated, the results support only preliminary antioxidant and diabetes-related enzyme-inhibition activity and warrant further controlled investigation.