Carbon dots-based ratiometric fluorescent sensor with viscosity-regulated FRET efficiency for tracking viscosity changes in lysosome during ferroptosis

For various physiopathological processes, ferroptosis is a unique form of regulatory cell death and has been confirmed to be closely related to intracellular viscosity fluctuations. The dysfunction of lysosome has been considered as one of the main causes of ferroptosis. For further understanding the occurrence and development of ferroptosis, it is of great significance to reveal the viscosity fluctuations of lysosome during ferroptosis. However, it is still lack of self-calibrating ratiometric probe with high accuracy and precision for effectively tracking the viscosity changes in lysosome during ferroptosis. In this work, a ratiometric fluorescent sensor based on the rhodol decorated carbon dots (m-CDs-Rho) was developed to track viscosity changes in lysosome during ferroptosis. The great capacity for targeting lysosome may be ascribed to the rich amino groups on the surface of m-CDs-Rho. The m-CDs-Rho nanosensor exhibits a sensitive linear response in the viscosity range of 6.33–718 cP with the advantages of high selectivity and remarkable photostability. The enhanced Förster resonance energy transfer (FRET) efficiency (increase from 5.4 % in PBS to 23.4 % in 90 % glycerol) and restricted motions of Rho are responsible for the ratiometric fluorescence response toward viscosity. Moreover, the well-separated fluorescence emission makes the developed nanosensor be suitable for high resolution bioimaging of the lysosomal viscosity. The cell imaging results suggest that m-CDs-Rho mainly distributed in lysosome, and the change of viscosity in the ferroptosis model are visualized successfully.