Asymmetric heptamethine quinocyanines with large Stokes shifts for high-fidelity imaging of mitochondrial viscosity and NAFLD.

Mitochondrial viscosity is a key parameter reflecting the functional status of mitochondria, and its dysregulation is linked to various diseases. In this study, we designed and synthesized two asymmetric heptamethine quinocyanine dyes (QCy7-1 and QCy7-2). QCy7-1 exhibits viscosity-activated fluorescence (λem = 780 nm; Stokes shift = 239 nm) and a 20.8-fold brightness increase in glycerol versus PBS. Probe QCy7-1 enables real-time monitoring of mitochondrial viscosity changes induced by nystatin, monensin, lipopolysaccharide, and starvation, and in vivo imaging of non-alcoholic fatty liver disease.