A novel amide-quinoline salt-based mitochondrial-targeted fluorescent probe for detecting pH in cells and water...

Mitochondria is the primary organelle responsible for energy production, and their weakly alkaline microenvironment (pH ≈ 8) is closely linked to cellular metabolism and disease states. Mitochondrial acidification is closely associated with the pathogenesis of a spectrum of disorders, encompassing neurodegenerative syndromes, cardiovascular disorders and cancer. Therefore, monitoring mitochondrial pH fluctuations is crucial for deciphering cellular physiological processes. In this research, we constructed a novel pH fluorescent probe QAA based on amide-quinoline salt, featuring piperazine as the pH recognition site and quinoline salt as the mitochondrial targeting group. QAA exhibited excellent water solubility (PBS buffer) which could be well matched with the cell imaging conditions, appropriate pKa (8.0) and mitochondrial targeting. Fluorescence spectroscopy results indicated that QAA possessed high selectivity and sensitivity, with a linear response in pH range of 6.6 to 9.5. The recognition mechanism was confirmed by density functional theory (DFT) calculations and HNMR spectral. Crucially, QAA not only exhibited excellent photostability, low cytotoxicity and the ability to detect pH in cellular mitochondria, but also could be used for real water sample detection, achieving recovery rates ranging from 98.96% to 104.84%. QAA held practical potential as a mitochondrial pH indicator for studying physiology-related processes involving mitochondria.