A dual channel fluorescent probe with pH-based specificity to lysosomes for multicolor imaging and localization

Abstract

We herein innovatively constructed the pure pH-dual channel probe DNOXA by the reaction of oxalyl chloride with 4-dimethylaminobenzaldehyde. DNOXA has two response sites for acidity, which are corresponding to pH-dual channel responses. When adding acid to pH 5.0, the protonation in the response site I enhanced the push-pull effect, and the absorption maxima of the optical spectra bathochromically shifted from 463 to 652 nm. When sequentially adding acid to pH 1.6, the response site II is awakened to work. The enhanced push-pull system was interrupted, and the absorption maxima hypochromatically shifted from 652 to 506 nm. In this process, the ratiometric change in the probe can be observed by naked-eye. Furthermore, quantum-chemical study well explained and supported the difference of their maxima absorption. Based on the excellent response of DNOXA to pH in vitro, DNOXA had commendable specific imaging and localization ability for lysosomes, undergoing dual channel images of protonation at the acidic microenvironment.