A Mitochondria-Targeted Ratiometric Fluorescent pH Probe

The pH of mitochondria (pH_m) is crucial in physiological processes. Here, we report a new mitochondria-targeted ratiometric pH-sensitive fluorescent probe for monitoring the mitochondrial pH change. This probe, IR-ANNA, was constructed by coupling a pH-sensitive naphthalimide derivative ANNA and a mitochondria-targeted pH-insensitive cyanine dye. IR-ANNA showed good mitochondria-targeted ability, excellent pH response, and low cytotoxicity, which makes IR-ANNA suitable for monitoring pH_m in living cells. Moreover, IR-ANNA has been successfully applied for monitoring the pH change of mitochondria under the stimuli of FCCP, NAC, and H₂O₂ in living cells.