A ratiometric fluorescent probe based on carbon dots assembly for intracellular lysosomal polarity imaging with wide range response

Lysosomal polarity is considered a key indicator of lysosomal function due to its significant impact on membrane fluidity and enzymatic reactions in lysosomes. Monitoring lysosomal polarity can gain insight into the related physiological and pathological processes and develop new diagnostic methods. However, current fluorescent probes with lysosomal polarity response suffer from narrow linear range, photobleaching and complicated preparation. Herein, a ratiometric fluorescent probe (r-bCDs) for intracellular lysosomal polarity imaging is designed and constructed by amide bond assembly of polarity-sensitive red fluorescent carbon dots (rCDs) and referenced blue fluorescent carbon dots (bCDs). r-bCDs show a much wider linear range of polarity response (orientation polarizability Δf from 0.020 to 0.315) than other probes, and the interference of uneven distribution and instrument factors can be effectively eliminated by ratiometric fluorescent sensing. Imaging of intracellular lysosomal polarity with r-bCDs is implemented to observe the polarity variation caused by the change of cell state and the difference between cancer cells and normal cells. This work provides a promising tool for studying the related physiological and pathological processes and developing new diagnostic methods.