A remarkable membrane-permeable fluorescent probe for real-time imaging of mitochondrial SO₂ with high fidelity during ferroptosis

Mitochondrial sulfur dioxide (SO₂) plays a double-edged role in cells, and the real-time and in situ tracing of its dynamic behaviors to elucidate its complicated functions in detail is of great significance. Here, we developed a simple mitochondria-targeted fluorescent probe ZW for tracing SO₂ with good membrane permeability. In probe ZW, the 1-phenylpyrrolidine-decorated benzopyrylium unit is employed as the selective response site for SO₂. Besides, it also acts as the main fluorophore for signal conversion. The spectral results displayed that ZW could emit near-infrared (NIR) fluorescence (670 nm) and has a highly sensitive and selective response to SO₂ (LOD = 0.19 μM). For biological imaging, compared with the control probe ZE, concentration- and time-dependent results verified that probe ZW has remarkable cell delivery with low concentration (200 nM) and fast response time (3 min). Furthermore, the NIR emission of ZW rendered high-fidelity imaging in living cells. Owing to its positive charge, ZW showed favorable mitochondria-targeting properties by colocalization experiments. Probe ZW could detect SO₂ in real-time and in situ with high photostability in cells. Significantly, it has the ability to monitor the changes of endogenous SO₂ during ferroptosis.