Visualizing mitochondrial viscosity during ferroptosis by using a solvatochromic effect-decreased hemicyanine probe

Because the vinyl-bridged donor-p-acceptor (D-p-A) structure of hemicyanine dye is very sensitive to the change of microenvironmental viscocity, they were applied for measurement of viscosity change in living cells. As the optical properties of most reported hemicyanine derivatives were strongly influenced by the solvent-sensitive amino group or hydroxyl group within the fluorophore, the design of hemicyanine dye with weak solvent ef-fect for monitoring the change of viscosity in living cells is valuable. Herein, we developed a pyrene-and dehydropyridocolinium-containing fluorescent probe PyQz for monitoring the change of viscosity in mito-chondria during ferroptosis process. As the probe using a pyrene group without a solvent-sensitive amino group or hydroxyl group as the electron donor and a dehydropyridocolinium as a electron acceptor, compared to many hemicyanine dyes the probe showed an obviously decreased solvatochromic effect and good chemical stability. The probe exhibited a good stability, ca. 25-fold enhancement in response to 95% glycerol, fast response time (<10 s) and excellent mitochondrial targeting ability (Pearson's correlation coefficient 0.98).