Membrane-Activated Fluorescent Probe for High-Fidelity Imaging of Mitochondrial Membrane Potential

Mitochondrial membrane potential (Delta Psi(m)) is a key indicator of cell health or injury due to its vital roles in adenosine 5'-triphosphate synthesis. Thus, monitoring Delta Psi(m) is of great significance for the assessment of cell status, diagnosis of diseases, and medicament screening. Cationic fluorescent probes suffer from severe photobleaching or false positive signals due to the luminescence of the probe on non-mitochondria. Herein, we report a lipophilic cationic fluorescent probe [1-methyl-2-(4-(1,2,2-triphenylvinyl)styryl)-beta-naphthothiazol-1-ium trifluoromethanesulfonate (TPE-NT)] with the features of aggregation-induced emission and intramolecular charge transfer for imaging Delta Psi(m) in live cells. TPE-NT is enriched on the surface of the mitochondrial inner membrane due to the negative Delta Psi(m), and its fluorescence is activated in the high-viscosity microenvironment. The false positive signals of emission from TPE-NT on non-mitochondria are therefore effectively eliminated. Moreover, TPE-NT exhibits a Stokes shift of >200 nm, near-infrared (similar to 675 nm) emission, excellent photostability, and low cytotoxicity, which facilitate real-time imaging in live cells. Cell imaging confirmed that the probe can rapidly and reliably report mitochondrial depolarization (decrement of Delta Psi(m)) during cell damage caused by CCCP and H2O2 as well as mitochondrial polarization (increment of Delta Psi(m)) by oligomycin. Furthermore, the probe successfully detected the reduction of Delta Psi(m) in these cell models of hypoxia, heat damage, acidification, aging, inflammation, mitophagy, and apoptosis caused by hypoxia, heatstroke, lactate/pyruvate, doxorubicin, lipopolysaccharide, rapamycin, monensin, and nystatin, respectively.