Dual-excitation ratiometric fluorescent sensor based on nitrogen-doped carbon dots for visual and sensitive detection of 4-nitrophenol and curcumin in food

The widespread use of 4-nitrophenol (4-NP) and curcumin, although beneficial across numerous industries, poses potential risks to human health and the environment. Thus, creating a sensitive and straightforward detection strategy is crucial for the rapid monitoring of these pollutants. Herein, a nitrogen-doped carbon dots (N-CDs)-based dual-excitation ratiometric fluorescent probe is developed, capable of detecting 4-NP and curcumin. The N-CDs are prepared from tris (hydroxymethyl) aminomethane (Tris) and phloroglucinol via a facile hydrothermal method, exhibiting a strong cyan fluorescence centered at 497 nm under excitation at 399 nm and 469 nm. In the presence of 4-NP, the fluorescence excited at 399 nm is significantly quenched compared to that excited at 469 nm due to the inner filter effect (IFE) and static quenching, achieving a limit of detection (LOD) of 76 nM within a linear range of 0.076–110 μM. In contrast, curcumin induces nearly complete fluorescence quenching at both excitation wavelengths, resulting from the quenching mechanism of dominant IFE and partial fluorescence resonance energy transfer. This response allows for curcumin detection over a concentration range of 0.081–90 μM with a low LOD of 81 nM. Furthermore, a smartphone-assisted sensing platform is constructed for the visual detection of 4-NP and curcumin in actual samples, achieving LODs as low as 117 nM and 123 nM, respectively. Therefore, this work enhances the capability for multi-analyte monitoring in complex systems and provides a practical and instructive strategy for detecting 4-NP and curcumin.