A wearable microfluidic device integrated with a sensor and potentiostat for sweat sodium monitoring

Wearable sensing devices, including the application of human sweat monitoring, are currently gaining attention for noninvasive purposes such as fitness tracking and even disease diagnostics. However, these devices encounter challenges related to reliability and data accuracy. For instance, the challenges include the collection of limited sample volumes, the efficiency and continuous flow of the sweat sample collector, sensor reliability, and the accuracy and stability of the electrochemical device. A microfluidic device with micro-sized channels has been developed to improve sample volume for collecting limited sweat samples in the microliter range and to reduce contamination. It has also been optimized for effective sweat flow by utilizing a water-washable material, which provides the microfluidic device with a hydrophilic surface. The microfluidic device has been designed with a vertical channel that enhances gravitational force to facilitate continuous fluid flow, prevent backflow, and reduce the mixing of old and new sweat concentrations. The developed potentiostat, an electrochemical analyzer, has been designed with a compact and lightweight form factor suitable for wearable applications. This device accurately measures electrical current across a range from milli- to nanoamperes when the voltage is varied. Dummy cell tests showed that the electrical properties are stable, with both the commercial and developed potentiostats exhibiting similar curve shapes. In sodium measurement tests, the device demonstrates high-performance accuracy, supported by a 95% confidence interval from Bland-Altman analysis. Device variability is characterized by a coefficient of variation of less than 4% and an intraclass correlation of 0.998 in the 10 mM to 200 mM sodium ion range. The device also shows good selectivity for sodium ions in the presence of other interfering ions, as it shows a small mean difference for each different concentration. It exhibits good stability, with a small standard deviation of 7. The results from the exercise activity reveal a decrease in sodium levels from 112 nA to 91 nA within 10 to 30 minutes, corresponding to concentrations ranging from 101 to 67 mM. This decrease aligns with the expected loss of sodium in the human body over time. In conclusion, the proposed wearable devices offer continuous flow capabilities and accurate sweat sodium measurements, addressing key challenges in current wearable technologies.