Single-/Dual-Responsive pH Fluorescent Probes Based on the Hybridization of Unconventional Fluorescence and Fluorophore for Imaging Lysosomal pH Changes in HeLa Cells

As a weak acidic organelle, lysosomes maintain acidic pH ranging from 4.5 to 5.5 and abnormal lysosomal pH levels can result in functional deficiency of lysosomes. Tracking the pH changes in lysosomes will help us to understand lysosome-related biological processes and diseases. However, pH-stimuli-responsive polymer-based lysosomal pH fluorescent probe with good water solubility and biocompatibility have rarely been reported. In this work, on the basis of naphthalimide chromophore and poly(N,N-dimethylaminoethyl methacrylate), we designed lysosome-targeted fluorescent probe NapBr-PDM or NapMl-PDM with single- or dual-responsive sites for monitoring pH changes in lysosomes. Both NapBr-PDM and NapMl-PDM exhibited a narrow polydispersity index, excellent fluorescence properties, water solubility, and high photostability. The synthesized probe NapBr-PDM, with a single-responsive site, showed fast response to pH changes and well-stained lysosomes, which could monitor lysosomal pH changes in cells after incubation with chloroquine. NapMl-PDM had good lysosomes-targeting property and highly sensitive response to pH, which could track lysosomal pH changes. Moreover, NapMl-PDM achieved tracking of lysosomal pH changes in cells during lysosomal storage disorder induced by high-concentration sucrose solution for the first time. Therefore, this work provided useful tools for monitoring intracellular pH changes as well as studying the relationship between lysosomal pH and its related diseases.