pH-Controlled Nanoparticles Formation and Tracking of Lysosomal Zinc Ions in Cancer Cells by Fluorescent Carbazole-Bipyridine Conjugates

Abstract

Fluorescent probes for simultaneous detection of multiple organelle specific analytes in cancer cells are essential for bioimaging applications. During abnormalities in cells, among other important parameters (metal ions, reactive oxygen species (ROS), enzymes, etc.) pH and Zn2+ are also altered in cells. Herein, we report the formation of nanoparticles of the fluorescent molecules based on carbazole-bipyridine conjugates (CBL1-3) and their use as nanoprobes to simultaneously detect Zn2+ and pH variations in lysosome. Upon increasing the pH from 4–6, these probes form nanoparticles with increased size and enhanced fluorescence at 510 nm. Among CBL1-3, nanoparticles of CBL2 upon Zn2+ binding, exhibit pH responsive intensity change only at lysosomal pH window at 610 nm and become silent above pH 7. Fluorescent imaging experiments on cancer cells revealed that the CBL2 nanoprobe is capable of localizing at lysosomes and facilitates the detection of endogenous Zn2+ and pH variations. Furthermore, the lysosomal Zn2+ variation with external stimuli induced programmed cell death was visualized using the nanoprobe.