Wearable flexible magnetoelastic sensor based on PDMS/chitosan/FeSiB/CNTs composite film for non-invasive real-time monitoring of uric acid in sweat.

Wearable non-invasive sensors enable continuous detection of uric acid in sweat, thereby facilitating the diagnosis of diseases related to renal and hepatic disorders. Nevertheless, the low uric acid content in human sweat and limitations of current sweat sampling strategies pose major challenges to the development of high-efficiency wearable uric acid sensors. Herein, we report a wearable flexible magnetoelastic (ME) sensor structurally integrated with a functional thin film based on PDMS/Chitosan/FeSiB/CNTs for monitoring uric acid in sweat. The integrated microfluidic patch designed in this work not only achieves sweat collection and directional drainage but also serves as a stable carrier to secure the thin film and magnet. Benefiting from the ME response of FeSiB magnetic particles incorporated inside the thin film, the sensing signal can be significantly amplified by an external magnetic field, which substantially enhances the detection sensitivity toward trace uric acid in sweat. Specifically, one side of the film is designed as a conductive layer, and the other side acts as a biomolecule-modified layer, ensuring that the two functional layers operate independently without mutual interference. Benefiting from this optimized structure, the proposed sensor was employed for testing in simulated sweat and in vivo human trials. Experimental results demonstrate the favorable performance of the sensor for real-time uric acid monitoring in sweat, with a detection limit of 1.2 μM and a wide linear detection range of 20-80 μM, and in the standard uric acid sample, the sensor showed a wider linear range of 10-200 μM, covering the physiological concentration range of uric acid in human sweat. Spiking tests in simulated sweat yielded recoveries from 94.1% to 114.3%, validating its high accuracy. The self-developed portable resistance measurement unit (5 × 5 cm) exhibited a mean relative error of only 0.34% compared with standard instruments, enabling reliable on-site measurement. In vivo tests on healthy volunteers further revealed distinct diurnal variations in sweat uric acid levels, confirming the sensor's great potential for non-invasive and real-time health management. The biosensor presents a promising avenue for uric acid monitoring using adaptable and user-friendly technologies.