Near-Infrared Nanothermometer Reveals Temperature Discrepancy between Organs and Body Surface for Heatstroke Prevention

Organ temperatures often vary significantly from body surface temperatures during heatstroke, leading to acute organ failure, although body temperature is continuously controlled. However, the exact temperature discrepancy between them remains unclear due to a lack of noninvasive techniques for real-time monitoring of organ temperature fluctuations. Herein, we developed a near-infrared emissive nanothermometer by codoping Nd³⁺ and Yb³⁺ to produce two distinct emissions at 980 and 1330 nm under 808 nm excitation. These emissions demonstrated differential responses to temperature variations, enabling the construction of a ratiometric nanoprobe for accurate temperature detection. Notably, the nanoprobe rapidly accumulated in mouse liver after intravenous injection, revealing that liver showed consistently higher temperature than rectum by approximately 1.5 °C. Moreover, liver injury was found to begin at a rectal temperature of 42 °C, rather than the 43 °C conventionally used in heatstroke models. These findings introduce a robust nanothermometer for accurately understanding the pathological progression of heat-related illnesses.