N-Doped Carbon Dots as a Fluorescent Probe for the Detection of Vitamin D

Vitamin D has a crucial role in the human body, and it regulates several important cellular activities throughout the body to improve health conditions. In this work, for the first time, we report a carbon-dot (CD)-based fluorometric technique for easy detection of vitamin D 3 (vit-D 3 ). A microwave-assisted hydrothermal technique was employed to produce highly luminescent carbon dots (CDs) in 2 min from mulberry ( Morus nigra ) juice. A simple “turn-off-on” fluorescent mechanism was used for the rapid detection of vit-D 3 . The photoinduced electron transfer (PET) mechanism-based quenching (turn-off) of fluorescence emission intensity of CDs was done using Ca 2+ ions. The fluorescence emission intensity was again recovered linearly in the presence of increasing vit-D 3 concentration (5 to 100 nM) and exposure to UV light. In this process, vit-D 3 attached to the carboxylic group of the CD surface through a UV light induced photocatalytic esterification reaction. The methodology has a good selectivity in the presence of various organic molecules and inorganic ions, glucose, starch, urea, amino acids ( l -cys), citric acid, lactic acid, and other vitamins, which are commonly found in human blood serum and in different food matrices. Finally, to evaluate the workability in real samples, multivitamins, pasteurized milk, fruit juice, and human blood serum samples were tested and found to have less than ∼0.5% relative standard deviation (RSD) compared to the concentration mentioned by the company or analyzed by other methods. This sensing technique has great significance, such as low cost, user-friendliness, and fast response for the detection of total vit-D (D 2 + D 3 ) in real-world samples.