A Stretchable Piezoelectric/pH Bimodal Sensor for Motion and Sweat Monitoring Using Polylactide/Polyester Elastomer/Carbon Quantum Dots Nanofiber

The rapid development of wearable electronics technology has provided considerable potential in the fields of motion monitoring and health management. However, current wearable sensors suffer from limitations of high stretchability to match the curvature deformation of human skin and function integration to realize simultaneous monitoring of multiple physiological signals. In this study, a stretchable bimodal piezoelectric/pH sensor is developed based on polylactide (PLLA)/polyester elastomer (PE)/carbon quantum dots (CQDs) composite nanofiber. The PE is synthesized to prossess an amorphous structure with a low glass transition temperature and mass of C═O dipoles, ensuring high stretchability and piezoelectricity, while the CQDs are designed with capacity to respond to pH variation by color change. The PE and CQDs were further blended with the PLLA matrix using electrostatic spinning technology to construct a nanofiber sensor with a bionic sponge structure. Ultimately, a PE–PLLA/CQDs–5% composite nanofiber film (PPC-5% film) shows a piezoelectric coefficient (d33) of 7.27 ± 0.05 pm/V, a wide range of pH responding capacity (pH = 3–7), a tensile strength of 4.40 MPa, and a recoverable elongation over 25%. This design not only enhances its stretchability but also ensures the sensor to realize simultaneous monitoring of motion and sweat by its sensitive piezoelectric and pH response. Thus, this flexible sensor with piezoelectric and pH bimodal response function, excellent biocompatibility, and wearable comfort provides an approach for the development of high-performance wearable sensors.