A Reliable Fiber-Optic Temperature Sensor Based on Fluorescence Intensity Ratio Technique for Real-Time Human Thermal Detection

In this paper, we propose and demonstrate a ratiometric fluorescence temperature sensor based on an innovative silica-tellurite composite, which is capable of sensing dynamic human thermal information in real time. The temperature-sensitive upconversion fluorescence emission is generated by a miniaturized tellurite glass tip upon near-infrared excitation and collected by silica optical fiber channels. The ambient temperature information is demodulated via a fluorescence intensity ratio technique. This is the first time that Er3+/Yb3+ co-doped tellurite glass, which has fragile mechanical strength and a distinctive softening temperature, has been successfully extracted into a thin-walled silica tube using a negative pressure method. This provides a robust packaging for tellurite glass, allowing it for reliable thermometry in various complex scenarios. When applied to a human body, the sensitive tip located in the armpit and tongue fossa can continuously and accurately acquire the thermal information with a fast response time within 1 s. With its miniature size, robust packaging, intrinsic safety, fast response, and high reliability, the proposed ratiometric fluorescence sensor holds great potential for real-time human (in vivo/ex vivo) health assessment in clinical medicine, personalized healthcare, human-machine interfaces, and other intricate scenarios.