A bifunctional sensitive fluorescence probe based on pyrene for the detection of pH and viscosity in lysosome

Lysosome is one of the important organelles in intracellular transport. It plays a significant role in the physiological process. The lysosomal microenvironment affects the functions of lysosome. When the original acidic environment of lysozyme is destroyed or the fluid viscosity increases gradually, various diseases are easily induced. However, most fluorescent probes can only locate in cells. The fewer probes of subcellular organelles were found and their functions are often single. So, it is of great importance to design multifunctional fluorescent probes with the capable of localizing in lysosome. In this study, a novel lysosome probe, 4-(4-Pyren-1-yl-but-3-enyl)-morpholine (PIM), was synthesized using pyrene as a fluorescent group and morpholine as a target group. The introduction of morpholine group made PIM localize in lysosome with high selectivity. The fluorescence will be enhanced with the increased viscosity because of restricting the rotation of CC bond and CN in PIM, and the detecting linear range is from 4.05 cP to 393.48 cP, which qualified the requirement of the viscosity monitoring in body. Meanwhile, the fluorescence intensity of PIM declines with the decrease of pH because the Schiff base of PIM is hydrolyzed, which was affirmed by ¹H NMR, LC-MS and fluorescence spectra. Moreover, cell imaging and MTT experiments confirmed that PIM as a novel bifunctional probe can be used to detect pH and endogenous viscosity in lysosome.