Ratiometric nanothermometer in vivo based on triplet sensitized upconversion

Temperature is an essential factor that counts for living systems where complicated vital activities are usually temperature dependent. In vivo temperature mapping based on non-contact optical approach will be beneficial for revealing the physiological phenomena behind with minimized influence to the organism. Herein, a highly thermal-sensitive upconversion system based on triplet-triplet annihilation (TTA) mechanism is pioneered to indicate body temperature variation sensitively over the physiological temperature range. The temperature-insensitive NaYF₄: Nd nanophosphors with NIR emission was incorporated into the temperature-responsive TTA-upconversion system to serve as an internal calibration unit. Consequently, a ratiometric thermometer capable of accurately monitoring the temperature changes in vivo was developed with high thermal sensitivity (~7.1% K^-1) and resolution (~0.1 K).