Hemicyanine based naked-eye ratiometric fluorescent probe for monitoring lysosomal pH and its application

Lysosome as the typical acidic organelle involved in many biological processes, the dysfunction of its pH would alter many diseases. Small-molecule fluorescent probe has been considered as vital tool for monitoring pH fluctuation in living cells. Herein, a hemicyanine based ratiometric fluorescent probe was synthesized, namely, 2,3-trimethy-3-[2-(dimethyl-amino-4-yl) vinyl]-3 H -benzo[ e ]indole ( BiDL ), for rapidly detection pH under acidic conditions. BiDL exhibited ratio fluorescence emission ( F 534nm / F 622nm ) characteristic with p K a 4.25. BiDL showed good linearly response in pH 3.4–4.82, indicating that the probe can be used for quantitative detection pH. The probe also displayed large Stokes shift (112 nm/201 nm) under neutral and acidic conditions, respectively, which could effectively reduce the excitation interference. BiDL had excellent cell membrane permeability , good photo-stability and low toxicity in living cells. The dual-channel confocal fluorescent microscopic ratiometric imaging application of pH in HeLa cells and lysosome were achieved successfully, indicating that BiDL has good potential for investigating lysosome-relevant pathological and physiological processes.