Fluorescence imaging of SO2 derivatives in Daphnia magna with a mitochondria-targeted two-photon ratiometric fluorescent probe

- A two-photon ratiometric fluorescent probe TP-SO2 was proposed based on carbazole dye platform.
- Probe TP-SO2 showed excellent sensitivity (0.161 μM), high selectivity and rapid response (35 s).
- Probe TP-SO2 was successfully applied to the detection of mitochondrial SO2 in living Hela cells.
- Probe TP-SO2 was used to monitor SO2 changes in Daphnia magna by two-photon fluorescence microscopy for the first time.

Sulfur dioxide (SO2), one of the reactive sulfur species (RSS), plays significant roles in various physiology and pathological processes. Excessive inhalation of SO2 will be conducive to the occurrence of respiratory diseases, neurological disorders and cardiovascular diseases, even lung cancer. Hence, it's vital to develop efficient methods for real-time monitoring of SO2in vivo. In this work, a two-photon ratiometric fluorescent probe TP-SO2 was proposed based on Michael addition mechanism, which showed a 143-fold enhancement of fluorescence intensity ratio (F483nm/F600nm) toward SO2 with outstanding sensitivity (DL 0.161 μM), rapid response (35 s) and high selectivity. Probe TP-SO2 showed good cell membrane permeability and localized in mitochondria. More importantly, to the best of our knowledge, it is the first time that the probe TP-SO2 was used for visualizing exogenous SO2 derivative changes in Daphnia magna through two-photon fluorescence microscopy, which is of great importance for biological research.

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