A fluorescent probe for detecting and imaging sulfur dioxide derivatives <i>in vitro</i> and <i>in vivo</i>

Sulfur dioxide (SO₂), an important gaseous signaling molecule, takes part in multiple pathological and physiological processes and plays a vital role in complex biological systems. However, the pathogenesis of many serious diseases, such as respiratory diseases, cardiovascular disorders and neurological diseases, resulting from excessive inhalation of SO₂ remains unclear. Therefore, it is significant to develop reliable analytical methods to effectively and concretely monitor SO₂ derivatives in living systems. In this study, a fluorescent probe BCy-SO2 was designed and synthesized for sensing SO₂ derivatives <i>in vitro</i> and <i>in vivo</i>. The developed probe BCy-SO2 is based on the semicarbocyanine fluorescent group BCy linked to benzaldehyde, and the -CHO group can be used for the detection of SO₂ derivatives. SO₂ dissociates readily in water to bisulfite (HSO₃^-). As expected, HSO₃^- disrupts the photoinduced electron transfer (PET) of the probe BCy-SO2 to produce fluorescence, which is characterised by fast reaction time, low detection limit and high sensitivity. Our probe BCy-SO2 has been successfully designed for the detection of SO₂ derivatives (HSO₃^-) in living cells, zebrafish and mice. We envisage that BCy-SO2 could be a powerful and attractive chemical tool to detect SO₂ derivatives in biological specimens.