Nitrogen-Doped Carbon Quantum Dots for Tannic Acid Analysis in Complex Food Matrices

The rapid, sensitive, and cost-effective detection of tannic acid (TA) in complex food matrices is essential for improving food safety standards. To meet this demand, nitrogen-doped carbon quantum dots (N-CDs) were prepared using a one-pot hydrothermal reaction using L-malic acid, citric acid, and tris(2-aminoethyl) amine as precursors. The excitation wavelength of the N-CDs was 430 nm, and the emission wavelength was 490 nm. Transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, and X-ray diffraction (XRD) were used to characterize the prepared N-CDs, and the results revealed a uniform morphology and a nitrogen-rich surface structure. In addition, we found that the N-CDs exhibited excellent selectivity for TA, primarily attributed to the fluorescence quenching effect of TA on the N-CDs. Therefore, a fluorescent sensor for TA detection was constructed based on the N-CDs, with a linear detection range of 0.500-250 µM (R² = 0.99987) and a detection limit of 0.15 µM (S/N = 3). The practical applicability of the sensor was demonstrated by analyzing TA in beer, red wine, and apple juice, achieving recoveries ranging from 101% to 116% and RSDs between 3.0% and 5.4%. The fluorescence assay results were closely related to the HPLC-DAD validation results, highlighting the accuracy of the method. The N-CDs-based detection platform offers the advantages of simplicity, sensitivity, and reliability, providing a promising tool for routine TA monitoring in food safety applications.