The improvement of lysosome targetability with oligoethyleneoxy chains linked benzo[a]phenoxazine

In order to improve lysosome targetability of probes, fluorescent probes based on benzo[a]phenoxazine attaching different length oligoethyleneoxy chains were designed and prepared. Probes 2a-c containing N-pyridineium-3-yl exhibited almost ON-OFF near-infrared emission responses at 697-701 nm from pH 2.8 to 7.2, and the calculated pK_a values of 2a-c were 4.90, 4.92 and 5.03 respectively. More importantly, fluorescent imaging experiments indicated that probes 2a-c were all lysosome biomarkers for Ges-1 and HeLa cells, which was because the introduction of oligoethyleneoxy groups improved the biocompatibility of probes, so that the probes 2a-c were better transported to lysosomes via the endocytosis pathway of the cells. Moreover, the probe 2a was selected as a representative, which not only showed good reversibility and selectivity, but used to successfully image lysosomal pH increases induced by chloroquine.