The IMB-CNM develops a portable multiparametric sensor for continuous sweat analysis in athletes

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A team from the Institute of Microelectronics of Barcelona (IMB-CNM-CSIC) has developed a device capable of analysing, in real time, the pH and the levels of sodium (Na⁺) and potassium (K⁺) in sweat. Assembled on a flexible polymer substrate, the system is composed of silicon transistors, a solid-state electrode that allows the transport of electric charges (ions), and a series of layers made of two of the most common plastics (polyethylene and polypropylene) due to their low cost and versatility. This last element distinguishes it from similar technologies available on the market, as they usually do not include microfluidic components that facilitate the movement of sweat towards the sensors for continuous data acquisition.

Exercise triggers the body's thermoregulatory mechanism to produce sweat. This sweat, which is 99% water, electrolytes, and other metabolites, is a valuable source of information for monitoring the health of athletes and preventing the adverse effects of dehydration.

In recent decades, there has been an increasing demand for personalized, real-time health assessments during exercise. This has spurred the development of wearable devices, primarily using ion selective electrodes (ISEs). These electrodes, which use a solid-state membrane to selectively transport ions, are more durable and can be used in a wide range of applications.

Many of these devices are fabricated using printing technologies or, in more advanced cases, inkjet printing directly onto flexible substrates. While these methods are quick and easy to produce, they present some challenges, such as low stability over time and the inability to perform continuous measurements due to the lack of fluidic elements to drive sweat to the detection areas.

One of the main challenges of this work is the patch's ability to continuously measure biomarkers for more than an hour. As Cecilia Jiménez, researcher at IMB-CNM and coordinator of WeCare, highlights, "To date, no multiparametric devices have been described that can continuously measure biomarkers for this duration."

Meritxell Rovira, PhD and lead author of the study, was responsible for evaluating the device on athletes at the University Hospital of Lausanne (CHUV). During the process, "designing a rigorous protocol was key to obtaining accurate and reliable information, as thousands of internal and external factors influence sweat physiology," she emphasizes. "It was crucial to ensure that changes in sodium and potassium concentrations were truly related to the studied variables. From a technological standpoint, the biggest challenge was to ensure a continuous and real-time sweat flow over the sensors, which required optimizing the fluidic system to maintain a stable flow rate and prevent accumulation or saturation," she adds.

The results showed a progressive increase in sodium concentration with exertion and sweat rate, while potassium and pH levels remained constant. The data obtained was compared with discrete measurements from commercial devices and showed a strong correlation between both data sets and, therefore, confirming the effectiveness of the sensor in real-time monitoring of sodium, potassium, and pH biomarkers. The team also observed a good correlation between temperature data and sweat flow with the variation of biomarkers measured by the patch.

The research was conducted within the WeCare project, part of the Sinergia Program, funded by the Swiss National Science Foundation (SNSF). The objective was to evaluate the performance of this wearable patch during exercise through continuous monitoring of biomarkers in sweat, with a focus on improving the diagnosis of an athlete's condition during sports activities.