Fluorescence detection of intracellular pH changes in the mitochondria-associated process of mitophagy using a hemicyanine-based fluorescent probe.

Intracellular pH behaves as a vital parameter in the physiological and pathological processes. Novel small molecule probes for precise and dynamic monitoring of pH fluctuations in cellular physiological processes are still highly required. Herein, we present a hemicyanine-based probe (HcPH) detection of the pH changes during the intracellular process of mitochondria-associated autophagy. HcP-H exhibits highly reversible and ratiometric fluorescence detection of pH variation due to the deprotonation/protonation process, showing orange fluorescence (λem = 557 nm) in basic media (pH 8.0) and green fluorescence (λem = 530 nm) in acidic media (pH 6.2), respectively. Organelle localization experiment in HeLa cells demonstrates that this probe could selectively accumulate in mitochondria, showing almost overlap with that of Mito-Tracker Green FM. More importantly, Fluorescence imaging of HcP-H in HeLa cells subjected to the nutrient deprivation has demonstrated that this probe could monitor the intracellular pH changes in the mitochondria-associated process of mitophagy. It is clearly confirmed that HcP-H would serve as a promising fluorescent probe for tracing mitophagy in living cells.