An ICT-based fluorescent probe for ratiometric monitoring the fluctuations of peroxynitrite in mitochondria

Peroxynitrite (ONOO⁻) is a well-known reactive oxygen species (ROS) which closely involves in various physiological and pathological processes. It is reported that mitochondria are the major site of ONOO⁻ production. Normal level of ONOO⁻ benefits mitochondria biological functions, while its overproduction will induce oxidative stress, resulting in an imbalance of mitochondria homeostasis. Therefore, accurate monitoring of ONOO⁻ in mitochondria will be beneficial for elucidating the physiological metabolism and fluctuations of ONOO⁻. Herein, a novel mitochondria-targeted ratiometric fluorescent probe Mito-NA for ONOO⁻ was designed rationally by regulating its intramolecular charge transfer (ICT) effect. Once reaction with ONOO⁻, Mito-NA manifested remarkable ratiometric fluorescence changes (18-fold) with a large red-shift (∼104 nm) emission, which was ascribed to the enhanced ICT process caused by the elimination of the electron-withdrawing recognition group 3-(trifluoromethyl) cinnamic acid and the exposure of electron-donating hydroxyl on Mito-NA structure. Furthermore, Mito-NA exhibited satisfactory performances for ONOO⁻ such as good sensitivity (LOD =0.12 μM), high selectivity to ONOO⁻ over other ROS, fast response and good mitochondrial targeting. More importantly, Mito-NA was successfully applied for ratiometric imaging and monitoring the fluctuations of mitochondrial ONOO⁻ in living cells.