A two-photon iridium(III) complex probe for sensitive detection of SO₂ derivatives in living cell mitochondria

The derivatives of sulfur dioxide (HSO₃^-) formed in the biological environment play a vital role in the circulation system. Excessive SO₂ derivatives will cause serious damage to the living system. Herein, a two-photon phosphorescent probe based on Ir(III) complex (named as Ir-CN) was designed and synthesized. Ir-CN is extremely selective and sensitive to SO₂ derivatives with significant phosphorescent enhancement and increased phosphorescent lifetime. The detection limit of Ir-CN for SO₂ derivatives reaches 0.17 μM. More importantly, Ir-CN preferentially accumulates in mitochondria, so bisulfite derivatives can be detected at subcellular level, which enriching the application of metal complex probe in biological detection. In addition, both single-photon and two-photon images can clearly show that Ir-CN is targeted to mitochondria. Benefits from its good biocompatibility, Ir-CN may be used as a reliable tool to detect SO₂ derivatives in mitochondrion of living cells.