Abstract
Singlet oxygen is among the reactive oxygen species (ROS) with the shortest life-times in aqueous media because of its extremely high reactivity. Therefore, designing sensors for detection of 1O2 is perhaps one of the most challenging tasks in the field of molecular probes. Herein, we report a highly selective and sensitive chemiluminescence probe (SOCL-CPP) for the detection of 1O2 in living cells. The probe reacts with 1O2 to form a dioxetane that spontaneously decomposes under physiological conditions through a chemiexcitation pathway to emit green light with extraordinary intensity. SOCL-CPP demonstrated promising ability to detect and image intracellular 1O2 produced by a photosensitizer in HeLa cells during photodynamic therapy (PDT) mode of action. Our findings make SOCL-CPP the most effective known chemiluminescence probe for the detection of 1O2. We anticipate that our chemiluminescence probe for 1O2 imaging would be useful in PDT-related applications and for monitoring 1O2 endogenously generated by cells in response to different stimuli.
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Reactive oxygen species (ROS) have an increasingly recognized role in cell signaling and stress response.1 Among all ROS, singlet oxygen (1O2) is getting substantial attention,2 especially in view of the recent progress in the field of photodynamic therapy (PDT) for cancer treatment.3 Therefore, real-time monitoring of 1O2 under biologically relevant conditions is of great interest. Although the phosphorescence of 1O2 at a wavelength of 1270 nm can be directly observed,4 it is very challenging to detect small amounts of 1O2 by such methods because of the extremely low quantum yield under aqueous conditions.5 Alternative approaches were aimed to develop small-molecule reaction-based probes for 1O2;6 among them, fluorescent turn-on probes have appeared as the most sensitive.7 Several fluorescent probes were also suitable for the imaging of 1O2 in living cells.8 In general, chemiluminescence imaging might be advantageous over fluorescence imaging, since in chemiluminescence there is no need for light irradiation, and thus background signal is extremely weak.9 Explicitly, for the imaging of 1O2, the advantage of chemiluminescence over fluorescence is even more substantial, since the light used for excitation of the dye could induce 1O2 generation by itself.10