An amphiphilic fluorophore containing a acetate ionic group and a coumarin moiety on each side of the alkyl chain has been newly designed for a alkaline phosphatase sensor. Fluorescence changes up on the addiotion of various metal ions show that CPM has high selectivity for the Cu2+ ion over other metal ions tested via fluorescence, i.e. 90% fluorescence quenching. The system, the Cu2+ ion complexed CPM, shows fluorescence enhancement, 92.3% fluorescence recovery. The activity of alkaline phosphatase (ALP) was successfully monitored by real-time turn-off assay.