A long-wavelength and color-changed cellulose-based fluorescent sensor for Al³⁺ and its applications in detection and...

A cellulose ester-based fluorescent derivative (EC-HNCA) was successfully synthesized via the reaction between 3-hydroxy-4-(2-hydroxy-4-sulfo-1-naphthylazo)naphthalene-2-carboxylic acid and ethyl cellulose. The structural variations before and after the synthesis were systematically characterized by proton nuclear magnetic resonance (¹H NMR), fourier-transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD) techniques. EC-HNCA showed no intrinsic fluorescence in solution under 365 nm UV light, while strong pink fluorescence was distinctly observed upon the introduction of Al³⁺, revealing its excellent selectivity toward Al³⁺. Moreover, a favorable linear correlation was established between the peak fluoresence intensity (610 nm) and Al³⁺ concentration within the range of 0-6.5 × 10^-6 mol/L, with regression equation y = 225,461×-42,707 (R² = 0.9910). The limit of detection (LOD) was calculated to be 7.6 nM. The EC-HNCA + Al³⁺ complex displayed diverse light-emitting colors in different solvent media. Furthermore, the EC-HNCA + Al³⁺ system was applied to fluorescence imaging of vascular tissues in watermelon rind, and clear fluorescent imaging results were obtained. The detection solution containing EC-HNCA emitted prominent pink fluorescence after adding Al³⁺ (0.5 × 10^-5 mol/L), which could be utilized for the determination of Al³⁺ in fresh white radish, garlic, Moso bamboo shoots, and Chinese cabbage. Consequently, EC-HNCA held great potential for further applications in plant tissue fluorescence imaging and detection of Al³⁺.