Flexible and Stretchable Electrochemical Sensor Merging the Multifunction of Monitoring Movement and Rapid Visual Signal Transmission

Noninvasive detection sensors for comfort and moisture absorption are popular for personalized health monitoring, yet integrated sensors that enable the on-demand detection of both physical and chemical indexes remain significantly challenging. Herein, we report a multifunctional fiber-based flexible sensing yarn for improved electrochemical and resistance sensing performance for in situ sweat activating and monitoring of body motion as well as the distinct color variation derived from the pH of sweat. The core–shell structure of the composite yarn (TSY) consists of a core layer of direct wet-spun twisted polyurethane fibers mixed with carbon black and a hydrophilic fiber layer of conductive zinc wires and colored lyocell fiber through the braiding method. The internal confined space between the core–shell layers can induce ion enrichment in sweat, enhancing the electrochemical sensing ability in capturing 0.5 μL of sweat, while the space-separated design can further isolate the interference so that pH and motion can be analyzed. Additionally, the colored hydrophilic lyocell fiber can transmit visual signals by the variance of color derived from the characterization of natural dyes in the process of adsorption of sweat. The designed TSY represents a promising integrated system capable of real-time monitoring of the chemical composition of sweat and the exercise conditions of movement.