A two-photon ratiometric fluorescent probe for the synergistic detection of the mitochondrial SO2/HClO crosstalk in cells and in vivo.

Known as a new member of the reactive sulphur species (RSS), endogenous sulfur dioxide (SO2) plays potentially reductive roles such as antioxidation, anti-aging, anti-inflammation, and cytoprotection; however, SO2 is also a metabolite of antioxidation. Hypochlorous acid (HClO) has powerful bio-effects on the innate immune system, and its uncontrolled production leads to adverse damage in cells. To illuminate the potential crosstalk between SO2 and HClO in redox homeostasis, we designed a two-photon ratiometric fluorescent probe for dual-response to mitochondrial SO2/HClO crosstalk in cells and in vivo. Our probe can effectively achieve ratio-type fluorescence dual-response to SO2 and HClO with desirable properties such as large two-photon absorption cross sections, rapid response times (SO2 < 50 s, HClO < 20 s), high sensitivities (limit of detection 8.0 nM for SO2 and 15.2 nM for HClO), and favorable selectivity. The probe has been successfully applied to quantitatively detect endogenous SO2 and HClO in HeLa and Raw 264.7 cells. We have verified that there exists a crosstalk between SO2 and HClO during the process of oxidative stress in mitochondria. We have also detected that SO2 can be endogenously produced through oxidation of intracellular sulfur-containing amino acids by HClO in zebrafish in real-time.