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 Cu²⁺/Cu⁺ ions and could image Cu²⁺/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.