Wearable Potentiometric Sensors Based on Commercial Carbon Fibres for Monitoring Sodium in Sweat

The use of commercial carbon fibres (CCF) to build wearable potentiometric sensors for the real-time monitoring of sodium levels in sweat during exercise is presented. CCF are an attractive substrate for building wearable electrochemical sensors because of their good electrical conductivity, chemical inertness, flexibility and mechanical resilience. In the first part of this work, the analytical performance of these novel potentiometric ion-selective electrodes made with CCFs is presented. Then, through the incorporation of a solid-contact reference electrode, the development of a complete miniaturized potentiometric cell with a Nernstian response (59.2 +/- 0.6mV/log [Na+], N=4) is obtained. Finally, the cell is integrated into a wearable patch and attached onto the skin of an athlete. The analytical characterization of the wearable patch shows a near-Nernstian response (55.9 +/- 0.8mV/log [Na+], N=3) for sodium levels from 10(-3)M to 10(-1)M in artificial sweat, well within the physiological range of interest. The device shows low noise levels and very good stability (-0.4 +/- 0.3mVh(-1)). To improve the usability of the sensor in real scenarios, a calibration-free approach is also explored. This platform opens new and attractive avenues for the generation of meaningful personalized physiological information that could be applied - among many other fields - in sports, nutrition and healthcare.