An activity-based fluorescent sensor with a penta-coordinate N-donor binding site detects Cu ions in living systems.

An activity-based sensor afforded a 63 times fluorescence-enhancement with Cu 2+ /Cu + ions and could image Cu 2+ /Cu + in living cells and in a multicellular organism. The sensor functioned only in the presence of ambient dioxygen and glutathione, and the characterization of intermediates and products hinted toward a sensing mechanism involving a Cu II hydroperoxo species.