Near-infrared emission viscosity-sensitive fluorescent probe for wash-free and specific targeting mitochondria

As a crucial indicator of the mitochondria micro-environment, viscosity profoundly influences various physiological activities of living cells. Numerous diseases are associated with an abnormal elevation in mitochondrial viscosity. Consequently, visualized monitoring of alterations in mitochondrial viscosity holds paramount importance for investigating disease mechanisms. Herein, six compounds YX1-YX6 with D-π-A configuration on the basis of triphenylamine and indole moiety were designed and synthesized. Among them, YX1-YX4 was developed by introducing different end groups (hydroxyl, methoxy, methyl, methyl ester) onto the backbone of YX5, while YX6 was designed to connect triphenylamine and indole moieties through thiophene linkers. Spectroscopic property tests revealed that compounds YX1-YX6 exhibited long-wavelength absorption and emission in viscous glycerol, displaying high sensitivity to changes in viscosity. Particularly, the fluorescence emission wavelength of compound YX6 exceeded 700 nm, placing it within the near infrared region. Furthermore, bioimaging experiments demonstrated that compound YX6 specifically targeted mitochondria via wash-free procedure. Additionally, compound YX6 exhibited independence from mitochondrial membrane potential, and could effectively monitor changes in viscosity. Thus, compound YX6 may have significant biological value as a viscosity-sensitive probe for studying mitochondria in biomedical and clinical research on diseases.