A mitochondria-targetable fluorescent probe for sulfur dioxide detection and visualisation in living cells

Sulfur dioxide (SO₂) is a one of reactive sulfur species (RSS) that plays significant roles in many physiological processes. While abnormal levels of SO₂ in mitochondria have been related to various diseases. Hence, developing suitable fluorescent probe for monitoring SO₂ is significant in living organisms. In this research, we designed and synthesized a mitochondrial-target probe Mito-NPH featuring the graft of a strong electron-withdrawing 4-pyridiniumylacrylonitrile unit to an electron-donating naphthalenic unit that intramolecular charge transfer (ICT) process happened. The probe Mito-NPH underwent a nucleophilic addition of HSO₃^-/SO₃^2-to give fluorescent emission signal change from red to blue and exhibited specific response toward HSO₃^-/SO₃^2-over other analytes. Moreover, Mito-NPH showed ultrafast response rate (within 10 s) for HSO₃^-. Importantly, cell imaging results demonstrated that the probe can sense endogenous SO₂ in mitochondria.