Stretchable and upconversion-luminescent polymeric optical sensor for wearable multifunctional sensing

Stretchable sensors with multiple sensory functions are in high demand for healthcare monitoring and artificial intelligence. Despite recent advances in wearable electronic sensors, it remains a significant challenge to achieve simultaneous sensing of both thermal and mechanical stimuli with a single sensor while integrating high stretchability. Herein, a stretchable and multifunctional optical sensor (SMOS) with simultaneous readout of temperature and strain is developed for wearable physiological monitoring of the human body. The SMOS primarily consists of a stretchable optical sensing fiber made from polymer nanocomposites containing lanthanide-based upconversion nanoparticles (UCNPs). Temperature measurements are achieved by ratiometric intensity measurements of the dual-emission UCNPs upon near-infrared excitation. By virtue of the ratiometric detection, the temperature readout of the SMOS is independent of strain deformations, enabling stable and continuous measurements of skin temperature during body motions. Furthermore, deformation of the SMOS by stretching leads to detectable and reversible changes in its light transmission, allowing tensile strains to be simultaneously measured. As a proof of concept, we demonstrate the capabilities of the SMOS in real time and simultaneous detection of both skin temperature and motion activities of the human body.