▎ 摘　　要

Cholecalciferol (Vitamin D-3) is an essential fat-soluble vitamin for healthy bone and muscle. Vitamin D deficiency is often not diagnosed as symptoms do not appear for a long time leading to cause osteoporosis, diabetes, and cancer. Currently, the testing of vitamin D is performed in sophisticated large-scale laboratories which are expensive and time-consuming for results. The development of a low-cost assay method could be helpful to detect vitamin D in limited-resource settings. Herein, for the first time, we report a novel electrochemical nanosensor for the analysis of vitamin D-3 in biological fluids based on the lanthanum nanoparticles-graphene quantum dots (LaNPs-GQDs) coupled with zeolitic imidazolate framework (ZIF-8) on a glassy carbon electrode (GCE) surface. For the construction of the LaNPs-GQDs@ZIF-8 sensing platform we have prepared low toxic graphene quantum dots (GQDs), lanthanum nanoparticles functionalized graphene quantum dots (LaNPs-GQDs), and zeolitic imidazolate frameworks (ZIF-8). The results revealed that the combined impact of all the prepared materials enhanced the catalytic activity of the sensor by increasing the surface area of the sensor, the electron transfer rate between the electrode and vitamin D-3 interface, and the facile oxidation of vitamin D-3. The morphological and structural characteristics of the prepared LaNPs-GQDs@ZIF-8 nanocomposite were investigated by field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), UV-vis spectroscopy (UV-vis), Fourier transform-infrared spectroscopy (FT-IR), and X-ray diffraction technique (XRD). Moreover, the electrochemical properties of the nanocomposite were examined by cyclic voltammetry, electrochemical impedance spectroscopy, chronoamperometry, and square wave voltammetry. Electrochemical studies revealed that an as-prepared sensor exhibited excellent electrochemical response towards vitamin D-3 oxidation over a wide linear range from 0.00625 mu M to 1.25 mu M with an acceptable detection limit of 0.00610 mu M respectively. Besides, the proposed sensing platform showed an excellent anti-interference nature, reproducibility, acceptable recovery, and reliable stability. Finally, the LaNPs-GQDs@ZIF-8@GCE sensor was successfully applied for the analysis of vitamin D-3 in real specimens to show its clinical applicability.