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).

Excessive or misplaced production of ClO(-) in living systems is usually associated with many human diseases. Therefore, it is of great importance to develop an effective and sensitive method to detect ClO(-) in living systems. Herein, we designed an 808 nm excited upconversion luminescence nanosystem, composed of the Nd(3+)-sensitized core-shell upconversion nanophosphor NaYF4:30%Yb,1%Nd,0.5%Er@NaYF4:20%Nd, which serves as an energy donor, and the ClO(-)-responsive cyanine dye hCy3, which acts as an energy acceptor, for ratiometric upconversion luminescence (UCL) monitoring of ClO(-). The detection limit of ClO(-) for this nanoprobe in aqueous solution is 27 ppb and the nanoprobe was successfully used to detect the ClO(-) in the living cells by ratiometric upconversion luminescence. Importantly, the nanoprobe realized the detection of ClO(-) in a mouse model of arthritis, which produced an excess of ROS, under 808 nm irradiation in vivo. The excitation laser efficiently reduced the heating effect, compared to the commonly used 980 nm laser for upconversion systems.

We designed and synthesized a water-dispersible dye-sensitized upconversion nanocomposite with approximately 17 times enhancement of upconversion luminescence. The nanocomposite was successfully applied in lymphatic imaging for the first time as an application model.