Dual-emissive carbonized polymer dots for the ratiometric fluorescence imaging of singlet oxygen in living cells

Singlet oxygen (1O2) isa type of reactive oxygen species (ROS), playing a vital role in the physiological and pathophysiological processes. Specific probes for monitoring intracellular 1O2 still remain challenging. In this study, we develop a ratiometric fluorescent probe for the real-time intracellular detection of 1O2 using o-phenylenediamine-derived carbonized polymer dots (o-PD CPDs). The o-PD CPDs possessing dual-excitation-emission properties (blue and yellow fluorescence) were successfully synthesized in a two-phase system (water/acetonitrile) using an ionic liquid tetrabutylammonium hexafluorophosphate as a supporting electrolyte through the electrolysis of o-PD. The o-PD CPDs can act as a photosensitizer to produce 1O2 upon white LED irradiation, in turn, the generated 1O2 selectively quenches the yellow emission of the o-PD CPDs. This quenching behavior is ascribed to the specific cycloaddition reaction between 1O2 and alkene groups in the polymer scaffolds on o-PD CPDs. The interior carbon core can be a reliable internal standard since its blue fluorescence intensity remains unchanged in the presence of 1O2. The ratiometric response of o-PD CPDs is selective toward 1O2 against other ROS species. The devel-oped o-PD CPDs have been successfully applied to monitor the 1O2 level in the intracellular environment. Furthermore, in the inflammatory neutrophil cell model, o-PD CPDs can also detect the 1O2 and other ROS species such as hypochlorous acid after phorbol 12-myristate 13-acetate (PMA)-induced inflammation.

Automated summary

A ratiometric fluorescent probe based on o-phenylenediamine-derived carbonized polymer dots (o-PD CPDs) was developed for real-time intracellular detection of singlet oxygen (1O2). The o-PD CPDs can produce 1O2 and selectively quench the yellow fluorescence, allowing for the selective detection of 1O2 against other reactive oxygen species (ROS). The probe was successfully applied to monitor 1O2 level in the intracellular environment and detect 1O2 and other ROS species in an inflammatory neutrophil cell model.