Construction of water-soluble fluorescent probes supported by carboxymethyl chitosan

Two novel Al³⁺ fluorescent probes, CMCS-P₁ and CMCS-P₂, were independently designed and synthesized by modifying the C-2 amino group of carboxymethyl chitosan with benzoyl hydrazide derivatives. The successful incorporation of the benzoyl hydrazide-derived probes was confirmed through FT-IR and ¹H NMR spectroscopy. The sensing performance demonstrated that CMCS-P₁ and CMCS-P₂ could selectively distinguish Al³⁺ from various metal ions, and the proposed probes both demonstrated excellent water solubility and exhibited a highly selective "turn-on" fluorescence response to Al³⁺ in pure aqueous solution. CMCS-P₁ exhibited a broad linear fluorescence response to Al³⁺ concentrations from 1.0 to 20.0 µM, featuring a detection limit of 0.33 µM, CMCS-P₂ displayed a more limited linear response in the range of 3.0-7.0 µM, with a detection limit of 1.0 µM. Additionally, a small-molecule fluorescent probe P₂ was synthesized to explore binding efficiency, and fluorescence imaging in living cells was conducted to successfully detect Al³⁺ with promising results.