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

Mitochondrial sulfur dioxide (SO) plays a double-edged role in cells, and the real-time and 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 SO with good membrane permeability. In probe ZW, the 1-phenylpyrrolidine-decorated benzopyrylium unit is employed as the selective response site for SO. 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 SO (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 SO in real-time and with high photostability in cells. Significantly, it has the ability to monitor the changes of endogenous SO during ferroptosis.