An Acylhydrazone-Based Fluorescent Sensor for Sequential Recognition of Al³⁺ and H₂PO₄

A novel acylhydrazone-based fluorescent sensor NATB was designed and synthesized for consecutive sensing of Al³⁺ and H₂PO₄^-. NATB displayed fluorometric sensing to Al³⁺ and could sequentially detect H₂PO₄^- by fluorescence quenching. The limits of detection for Al³⁺ and H₂PO₄^- were determined to be 0.83 and 1.7 μM, respectively. The binding ratios of NATB to Al³⁺ and NATB-Al³⁺ to H₂PO₄^- were found to be 1:1. The sequential recognition of Al³⁺ and H₂PO₄^- by NATB could be repeated consecutively. In addition, the practicality of NATB was confirmed with the application of test strips. The sensing mechanisms of Al³⁺ and H₂PO₄^- by NATB were investigated through fluorescence and UV-Visible spectroscopy, Job plot, ESI-MS, ¹H NMR titration, and DFT calculations.