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 Al3+ and F- in almost 100% aqueous medium was successfully designed and synthesized. The probe offers two binding pockets for Al3+ 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 Al3+ 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 Al3+ ion and 79 μM for F-) in drinking water. The probe L was successfully applied to the detection of Al3+ and F- in cells using fluorescence microscopy.