Indole-incorporated-benzoeindolium as a novel mitochondrial and ratiometric fluorescent probe for real-time tracking of SO2 derivatives in vivo and herb samples

Sulfur dioxide (SO2) has been regarded as a well-known environmental pollutant that can cause allergic respiratory responses and even serious diseases, whereas endogenous SO2 as an important gaseous signaling molecule is involved in many physiological and pathological processes. In addition, SO2 and its derivatives (bisulfite and sulfite) are also widely-used preservatives and antioxidants in various foods, beverages and pharmaceuticals, whose concentration level is strictly limited due to the adverse effect on community health. Thus, dynamical determination of SO2 and its derivatives both in vitro and in vivo is highly desirable. Herein, we reported a novel mitochondrial fluorescent probe indole-incorporated-benzoeindolium (InB) for SO2 derivatives with high sensitivity and selectivity in DMSO-H2O (2:3, v/v, 10 mM PBS, pH = 7.40) media. The probe exhibited low detection limit (4.39 nM) and rapidly responsive (300 s) recognition for SO2 derivatives in a ratiometric manner. The sensing mechanism could be attributed to the nucleophilic addition of the electron deficit carbon-carbon double bonds from the linker with HSO3-, resulting in inhibition of the ICT process of the probe after reaction, which was confirmed by high-resolution mass spectroscopy (HR-MS) and H-1 NMR techniques. Moreover, the probe was successfully applied to detect HSO3- in Dioscotea opposita Thunb and Gastrodia elata Bl, which represents one of the only two examples of using synthetic fluorescent probes to monitor SO2 derivatives in herb samples to date. Furthermore, its applications in real-time tracking and bioimaging of SO2 derivatives in living cells, zebrafish and nude mice were also achieved. Hopefully, this work provides a promising methodology for the design of other fluorescent probes for SO2 derivatives with tailored performance.