Supramolecular capture of highly polar amidosquaraine dye in water with nanomolar affinity and large turn-on fluorescence†

A supramolecular dye-capture system comprising anionic amidosquaraine guest and macrocyclic tetralactam host exhibits nanomolar affinity and ‘‘turn on’’ visible fluorescence. Utility is demonstrated with a new fluorescent assay for liposome leakage induced by the biomedically important enzyme phospholipase A2.