Efficient synthesis of red-emissive nitrogen-doped carbon dots for sensitive detection of amaranth in food samples

Red-emissive carbon dots (CDs) play a crucial role in various food detection applications due to their strong fluorescence in the red luminescence region. Typically, nitrogen-doped CDs are synthesized from diverse precursors and predominantly emit blue fluorescence, which limits their advancement. In this study, we developed an efficient strategy to synthesize novel red-emissive nitrogen-doped carbon dots (R-NCDs) from L-malic acid and urea using a simple solvothermal approach. The synthesized R-NCDs exhibited optimal excitation and emission wavelengths of 540 nm and 630 nm, respectively, and achieved a quantum yield of 14.3 %. Additionally, the fluorescence of the R-NCDs was effectively quenched by the food coloring agent amaranth, allowing for a linear range of 0.050–75 µM and a detection limit of 15 nM. Furthermore, we established a new and efficient fluorescence detection platform capable of detecting trace amounts of amaranth in soda, fruit gummies, hard candies, vodka, preserved fruits, juices, and cocktails, yielding recovery rates ranging from 88.0 % to 119 % with a relative standard deviation of 1.1–3.9 %. Notably, this study is unique as it presents the first synthesis of R-NCDs based on L-malic acid and urea for the detection of amaranth content in various food samples, emphasizing its novelty and significance.