A phenol-pyridylimine probe was utilized as an optical sensor to quantify the presence of aluminum ions using a turn-on fluorescence enhancement approach. The high sensitivity was the result of FRET amplification of the receptor subunit fluorescence emission. The complex stability constant (K s ) for the stoichiometric 1:1 complex of the sensor with aluminum ions was obtained by fluorimetric titration. Remarkably, fluorescence output was not significantly affected by other trivalent cations, particularly Ga 3+ and In 3+ .