Abstract
Stretchable sensors that can conformally interface with the skins for wearable and real-time monitoring of skin deformations, temperature, and sweat biomarkers are of profound significance for early prediction, diagnosis, and treatment of diseases. Integration of multiple modalities in a single stretchable sensor to simultaneously detect these stimuli would be beneficial for more sophisticated understanding of human physiology, but yet, has not been achieved. Here, we report a stretchable multimodal photonic sensor capable of simultaneously detecting and discriminating strain deformations, temperature, and sweat pH in a single sensor architecture. The multimodal sensing abilities are enabled by realization of multiple sensing mechanisms in a hydrogel-coated polydimethylsiloxane (PDMS) optical fiber (HPOF), featured with high flexibility, stretchability, and biocompatibility. The integrated mechanisms are designed to operate at distinct wavelengths to facilitate stimuli decoupling, and adopt a ratiometric detection strategy for improved robustness and accuracy. To achieve simplicity on sensor interrogation, spectrally-resolved multiband emissions are generated upon the excitation of a single-wavelength laser based on upconversion luminescence (UCL) and radiative energy transfer (RET) processes. We show that the sensor allows for simultaneous and sensitive detection of strain deformations, temperature, and pH levels in the physiological range with fast responsiveness, robust repeatability, and reliability. Furthermore, we demonstrate proof-of-concept applications of the sensor for simultaneously detecting artery pulse or cardiopulmonary activities, along with skin temperature and sweat pH with negligible crosstalk, enabling a new paradigm of wearable multiparameter monitoring in healthcare.