A Nanothermometer with a Microwave Thermal Effect for Sensing Cell Membrane Temperature and Measuring Microwave-Induced Thermal Gradient Distribution

In microwave (MW) thermotherapy, it is challenging to regulate the temporal and spatial distribution of the temperature at the nanoscale. Herein, we report a nanothermometer for simultaneous MW heating and temperature distribution measurement. The nanothermometer was prepared by free radical polymerization with vinylbenzyl trimethylammonium chloride (VBTMACl) as the MW thermosensitizer and isopropylacrylamide (NIPAM) as the thermoresponsive unit, followed by anion exchange with fluorophore sodium 3-(4-(1,2,2-triphenylvinyl)phenoxy)propane-1-sulfonate (TPESO₃Na). In aqueous medium, the nanothermometer self-assembles into micelles with TPESO₃^- as the hydrophobic core and thermoresponsive polymer P(NIPAM-<i>co</i>-VBTMACl) as the hydrophilic shell, thereby to exhibit aggregation-induced emission (AIE). By increasing the temperature, the conformational change of the thermoresponsive polymer drives TPESO₃^- to transfer from the core to the shell of the micelles, and the nanothermometer converts from an aggregate state to a dispersed state. As a result, the nanothermometer exhibits a superior temperature-dependent emission feature in the temperature range 25-41 °C, with a relative thermal sensitivity of 8.3% °C^-1 at 37 °C. In addition, the nanothermometer possesses a positive charge and balanced hydrophilic-hydrophobic feature which prompts its anchoring to the cell membrane. Therefore, it realizes in situ temperature sensing of cell membranes during MW heating, as well as temperature distribution of the cell membrane.