Phosphorescent Polymeric Thermometers for In Vitro and In Vivo Temperature Sensing with Minimized Background Interference

Temperature plays a crucial role in many biological processes. Accurate temperature determination is important for diagnosis and treatment of diseases. Autofluorescence is an unavoidable interference in luminescent bioimaging. Hence, a large amount of research works has been devoted to reducing background autofluorescence and improving signal-to-noise ratio (SNR) in biodetection. Herein, a dual-emissive phosphorescent polymeric thermometer has been developed by incorporating two long-lived phosphorescent iridium(III) complexes into an acrylamide-based thermosensitive polymer. Upon increasing temperature, this polymer undergoes coil-globule transition, which leads to a decrease in polarity of the microenvironment surrounding the iridium(III) complexes and hence brings about emission enhancement of both complexes. Owing to their different sensitivity to surrounding environment, the emission intensity ratio of the two complexes is correlated to the temperature. Thus, the polymer has been used for temperature determination in vitro and in vivo via ratiometric luminescence imaging. More importantly, by using the long-lived phosphorescence of the polymer, temperature mapping in zebrafish has been demonstrated successfully with minimized autofluorescence interference and improved SNR via time-resolved luminescence imaging. To the best of our knowledge, this is the first example to use photoluminescent thermometer for in vivo temperature sensing.