Characterization and Application of the Fluorescent APTA-nano Biosensors Based on CdTe-TGA QDs for Determination of 25-hydroxyvitamin D3

Medical studies have shown that vitamin D deficiency is strongly associated with several metabolic disorders, including diabetes, cardiovascular diseases, and cancer. So, it is crucial to regularly check its concentration in the blood serum. Traditional methods for detecting 25-hydroxyvitamin D₃ [25(OH)D₃] as a marker of vitamin D status are expensive, time-consuming, and require a skilled workforce and specialized laboratory. This study developed a simple and cost-effective fluorescence system for 25-hydroxyvitamin D₃ determination. The fluorescent APTA-nano biosensors were fabricated using cadmium telluride quantum dots modified with thioglycolic acid (CdTe-TGA QDs) and functionalized with thiol-25(OH)D₃-aptamer through ligand exchange. The thiol-25(OH)D₃-aptamer interacted directly with CdTe-TGA QDs, increasing fluorescence intensity. However, it decreased when the target molecules of 25-hydroxyvitamin D₃ were introduced. The structural and morphological characteristics of APTA-nano biosensors were confirmed by various analytical methods such as UV-visible spectroscopy, Fourier-transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), energy dispersive x-ray spectroscopy (EDX), transmission electron microscopy (TEM), and dynamic light scattering (DLS). According to the typical Stern-Volmer equation, the relationship between fluorescent quenching and target concentration was linear with a detection limit of 1.35 × 10^-8 M, a quantification limit of 4.50 × 10^-8 M, and a relative standard deviation of 1.75%. The optimized APTA-nano biosensor demonstrated high specificity towards the target and stability over 28 days. Furthermore, it detected 25-hydroxyvitamin D₃ in human serum with a recovery rate of up to 99.77%. The results indicate that the fluorescent APTA-nano biosensors could be valuable in developing robust sensing technology for low-concentrated analytes.