Fluorogenic and Genetically-Targeted Red-Emitting Molecular Calcium indicator

We introduce a strategy for the fluorogenic and genetic targeting of a calcium sensor by combining a protein fluorogen with the BAPTA sensing group. The resulting dual-input probe acts like a fluorescent AND logic gate with a Ca2+-sensitive red emission that is activated only upon reaction with the protein self-labeling tag HaloTag with a 18-fold intensity enhancement. The fluorogenic targeting of the calcium probe was evidenced by the selective wash-free imaging of calcium in the nucleus of Hela cells expressing a nuclear HaloTag protein.