Development of Reaction-free and Mitochondrion-immobilized Fluorescent Probe for Monitoring pH change

Abstract Mitochondrial pH is an indispensable parameter of reflecting mitochondrial function, and its abnormity is closely associated with various diseases, such as cardiovascular diseases, Alzheimer’s disease, and Reye's syndrome. For real-time and long-term monitoring of mitochondrial pH changes, we for the first time developed a free-reaction and mitochondrion-immobilized pH-sensitive fluorescent probe (MTpH). This probe consists of a cationic pyridinium for targeting mitochondrion, a long alkyl chain for fixing on the mitochondrion, and a morpholine-linked naphthalimide as a fluorescence turn-on signaling unit to pH change. By linking a long alkyl chain, probe MTpH could successfully immobilize on the mitochondrion in a reaction-free way, which efficiently avoided the irreversible destroy to the original structure and function of the mitochondrion. Importantly, this probe also showed a sensitive response to pH changes with the pKa of 5.77, allowing for monitoring mitochondrial pH changes in impaired mitochondria undergoing mitophagy. Therefore, the strategy in this context provides a new thought for designing mitochondrion-immobilized pH-sensitive probes and our probe MTpH is promising as a useful tool for long-term monitoring of mitochondrial pH changes.