A novel mitochondrion-targeted fluorescent probe for detecting viscosity in living cells and zebrafishes

Based on the twisted intramolecular charge transfer (TICT) mechanism, a new mitochondrion-targeted fluorescent probe CSS-1 for the detection of viscosity variations was developed. The probe showed a strong response to viscosity changes, the fluorescent intensity of the probe increased 18-fold from methanol to glycerol, and it exhibited a Large Stokes shift (135 nm in methanol and 117 nm in glycerol), good stability in the physiological pH range, and great photostabllity. The mechanism of the probe response to viscosity variations was confirmed by the density functional theory calculation. Moreover, probe CSS-1 could be localized at mitochondria (the colocalization coefficient was 0.85) and was successfully employed for the visualization of viscosity variations in HeLa cells and zebrafishes, which verified that the probe has potential for investigating viscosity variations in Living systems.