A Mitochondria-Targeted Fluorescent Probe for Nanomolar Cysteine Detection via an ICT Mechanism in Living Cells and Zebrafish

A mitochondria-targeting fluorescent molecule, (E)-2-(2-(7-(acryloyloxy)-2-oxo-2H-chromen-3-yl) vinyl)-3-ethyl-1,1-dimethyl-1H-benzo[e]indol-3-ium (BCA), was designed to detect cysteine (Cys). BCA undergoes a Michael addition with Cys, followed by cyclization and elimination, generating the intramolecular charge transfer (ICT)-active fluorophore and triggering a fluorescence turn-on response with emission maximum at 620 nm within 2 min. BCA exhibited good selectivity and a detection limit of 200 nM for Cys in the PBS buffer. Its biological applicability was demonstrated in HepG2 cells and zebrafish models.