A phenolphthalein-based fluorescent probe for the sequential sensing of Al3+ and F− ions in aqueous medium and live cells

A novel fluorescent probe , phenolphthalein‑dialdehyde‑(2‑pyridyl) hydrazone (L), for sequentially detecting Al 3+ and F − in almost 100% aqueous medium was successfully designed and synthesized. The probe offers two binding pockets for Al 3+ to form a 1: 2 ligand/metal complex, leading to a significant fluorescence enhancement at 465 nm. Further, the in-situ formed L-Al complex acts as a secondary fluorescent chemosensor for F − by quenching the fluorescence of the complex with high selectivity. The detection limit for Al 3+ and F − sensing is 2.28 nM and 0.13 μM, respectively, which are far below the World Health Organization (WHO) acceptable limits (7.41 μM for Al 3+ ion and 79 μM for F − ) in drinking water . The probe L was successfully applied to the detection of Al 3+ and F − in cells using fluorescence microscopy .