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-/SO32-to give fluorescent emission signal change from red to blue and exhibited specific response toward HSO3-/SO32-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.