Intracellular viscosity can be measured to reflect the state of living cells. Fluorescent probes are powerful tools for viscosity detection in vivo. Herein, we report on a novel red-emitting viscosity-sensitive probe DJH with a large Stokes shift of 165 nm, showing a 400-fold fluorescence enhancement from PBS solution to 90% glycerol. The probe was suitable for the visualization of the changes in viscosity within living cells and also in zebrafish treated with microplastics for the first time. Furthermore, the viscosity of fresh blood from diabetic mice and hypertensive and diabetic patients was first evaluated by using DJH. These results showed that the probe has a wide range of potential applications in basic research on environmental pollution and in the pre-diagnosis of patients.