A real-time ratiometric fluorescent probe for imaging of SO₂ derivatives in mitochondria of living cells

A real-time ratiometric fluorescent probe (IN-CZ) for highly selective detection of sulfite was designed and synthesized, which is based on modulating the intramolecular charge transfer (ICT) of the hemicyanine dye platform. The mechanism of using the probe is mainly through the Michael addition that occurs between IN-CZ and sulfite with a detection limit of 2.99 × 10^-5 M. IN-CZ displays a fast response (within 1 minute) and is highly selective for SO₃^2-/HSO₃^- over ROS, biologically relevant ions, biological mercaptans and other reactive species. More importantly, IN-CZ was suitable for ratiometric fluorescence imaging in living cells, by real-time monitoring of SO₃^2-/HSO₃^- changes in mitochondria targeted in living cells.