A self-calibrating phosphorescent polymeric probe for measuring pH fluctuations in subcellular organelles and the zebrafish digestive tract

The precise regulation of pH in biological systems, including intracellular organelles and tissues, is essential to the normal functions of vital movement. Accurate pH determination will contribute to a better understanding of related physiological processes and the effective monitoring of physiologic derangements. Luminescence imaging and sensing are useful tools for biological study. However, the conventional intensity-based detection method suffers from low signal-to-noise ratio. Herein, we report a water-soluble ratiometric phosphorescent probe (P-pH) for measuring pH fluctuations in biological samples based on ratiometric photoluminescence imaging and photoluminescence lifetime imaging. P-pH consists of a pH-responsive iridium(iii) complex, pH-inert iridium(iii) complex, and hydrophilic poly(N-vinyl-2-pyrrolidone). Owing to its dual emission, P-pH was successfully used to monitor the pH variation in mitochondria and lysosomes based on the ratiometric readout. Using P-pH, the reliable evaluation of three types of pH modifiers in the zebrafish digestive tract was also realized with a distinguishable long emission lifetime. This is the first example of assessing pH modifiers in real animal models using a luminescent approach.