Development of a Highly Sensitive Fluorescent Nanosensor for Curcumin and Vanillin Detection Using Nitrogen-Doped Carbon Quantum Dots

The sensitive and specific detection of curcumin and vanillin are important for food safety, quality control, and consumer health protection. Here, a nitrogen-doped carbon quantum dots (N-CQDs)-based nanosensor was developed for the highly sensitive detection of curcumin and vanillin. N-CQDs were synthesized via solvothermal method using L-theanine and 2,4,6-trimethyl-1,3-phenylenediamine (2,4,6-TMPDA) as carbon precursors. The excitation wavelength of the N-CQDs was 360   nm and the emission wavelength was 455   nm. The structural features of N-CQDs were characterized by FT-IR, X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD) and Raman spectroscopy. Subsequently, the effects of pH and NaCl concentrations on N-CQDs fluorescence were studied. More importantly, leveraging the quenched fluorescence for multi-molecule sensing, the selective and sensitive detection of curcumin and vanillin were achieved, with linear ranges of 0.010-50   μM and 0.10-50   μM, respectively, and LODs of 3   nM and 30   nM, respectively. Using the developed fluorescence method, curcumin in chicken essence samples and vanillin in montmorillonite powder, chocolate beans, high-mountain sugar, and plum sugar were quantified. The recovery rate for curcumin was 93.4-106%, and for vanillin was 93.0-110%. The measured contents were further validated by HPLC-UV. Overall, the high N-CQDs selectivity for curcumin/vanillin enables rapid, sensitive fluorescence food analysis.