Toward the detection of cellular copper(II) by a light-activated fluorescence increase

A new type of Cu2+ fluorescent sensor, coucage, has been prepared with a photosensitive nitrophenyl group incorporated into the backbone of a coumarin-tagged tetradentate ligand. Coucage provides a selective fluorescence response for Cu2+ over other biologically relevant metal ions. Coordination of Cu2+ dims the fluorescence output until irradiation with UV light cleaves the ligand backbone, which relieves the copper-induced quenching to provide a turn-on response. Experiments in live MCF-7 cells show that coucage can be used for detecting changes in intracellular Cu2+ upon the addition of excess exogenous copper. If improvements can be made to increase its affinity for copper, this new type of turn-on sensor could be used as a tool for visualizing the cellular distribution of labile copper to gain insight into the mechanisms of copper trafficking.