Simultaneous imaging of lysosomal and mitochondrial viscosity under different conditions using a NIR probe

Abstract This article reported a hemicyanine dye fluorescent probe (1), based on benzo[e]indole and aromatic azonia skeleton, for simultaneous detection of viscosity fluctuation in mitochondria and lysosomes. Probe 1 exhibited near infrared emission and high sensitivity towards viscosity of the medium. As the viscosity increases, the rotation of C-C single bond between the benzo[e]indole and the nitrogen heterocycle could be suppressed, and the entire molecular scaffold was coplanar and emitted strong fluorescence due to more delocalized electron distribution. The fluorescence intensity of probe 1 was enhanced 16.2 times at 650 nm as the viscosity increased from 0.89 cP to 865 cP. Correspondingly, the fluorescence quantum yield of probe 1 increased from 4.2% to 49.6%. The change of lg (I650nm) had a good linear relationship with lgη (viscosity values: 0.89 cP to 8.6 cP), which meant the viscosity of dilute solution could be detected quantitatively. In cell experiments, probe 1 with low concentration (500 nM) had stronger fluorescence intensity in cancer cells than in normal cells. Besides, probe 1 could monitor the viscosity changes of mitochondria and lysosomes caused by the addition of ionophores (monensin, nystatin and dexamethasone) or in the process of autophagy. The results provide a simple and effective method for the early diagnosis of related diseases.