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 pKa 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.

Rosamine with pyronine-pyridinium skeleton: unique mitochondrial targetable structure for fluorescent probes.

Two rosamine-based probes (1a-b) with pyronine-pyridinium skeleton were designed and prepared. Probe 1a bearing boron ester unit was oxidized and eliminated upon addition of hydrogen peroxide (H2O2), and the emission spectrum exhibited OFF-ON response accompanied by 33-fold fluorescent enhancement. In contrast, the fluorescence intensity of probe 1b enhanced 58 times after the dinitrophenyl ether part within the probe was removed by nucleophilic substitution with hydrosulfide (H2S). The design concept was based on the d-PET process in pyronine-pyridinium structures, and free 4-pyridinyl-substituted pyronine dye showing strong fluorescence was released followed by elimination. Furthermore, as biocompatible molecules, probes 1a-b have been successfully applied for imaging in live HeLa and Ges-1 cells, and all of them can serve as mitochondrial targetable probes in red channel for detecting independent species.

The pH-influenced PET processes between pyronine and different heterocycles.

The OFF-ON and ON-OFF type pH probes based on rosamine were designed by using the relative electron densities between pyronine and various linked heterocycles. Probe 1a with an indole-pyronine skeleton gave an OFF-ON pH response (pKa = 1.41) with decreasing pH, and the relative fluorescence intensity increased 15-fold, while probe 1b with an imidazole-pyronine skeleton did not give an ON-OFF response to different pH values. When pyronine was connected with a quinolinyl group, i.e., probes 1c-d, the red emission (around 575-800 nm) gave a monotonous ON-OFF pH response (pKa = 3.26 and 2.62, respectively) with decreasing pH. The relative fluorescence intensities decreased 263- and 46-fold, respectively. Changes in the electron donating abilities of the nitrogen containing heterocycles were used to explain variations in PET processes within the probes, and their pH-dependent PET mechanisms were verified using time-dependent density functional theory calculations. Confocal fluorescence imaging was also used to evaluate the potential biomedical application of probes 1a-d. Ultimately, probe 1d with an appropriate pKa value and good biocompatibility showed lysosome targeting ability.