Analysis of ammonium in human sweat during physical strain using a portable sensor device and enzymatic measurements are compared. The portable device is based on a screen‐printed electrolyte sensor connected with an evaluation board for data acquisition and transfer. During performance tests with artificial sweat, the sensor shows a low detection limit of 0.3 mM. Thus, the typical concentration range of ammonium in sweat lies within the working range of the sensor. We also demonstrate the necessity of the comparison measurement for verification of the correct performance of screen‐printed sensors and show how other components of human sweat influence the measured potential. Regarding the change in ammonium concentration during different levels of work out intensity, we point out a different behavior of what is expected physiologically. With this the importance of consideration of several parameters during sweating, like the sweat rate and other ingredients in human sweat, was demonstrated for correct determination of the ammonium concentration.

The measurement of physiological parameters in sweat has long been assumed to offer a non-invasive alternative to conventional blood testing. Recently, advances in sensor technology enable the production of printed sweat sensors applicable for the use in wearable devices. However, the remaining challenge is the determination of the physiological correlation between blood and sweat components. In this study, we conducted ammonia measurements in blood and sweat during a stepwise incremental cycle ergometer test in 40 subjects under completely controlled conditions in a clinical environment to determine the correlation between the ammonium concentrations in blood and sweat. Samples were taken for each workload step separately. Sweat was sampled directly from the upper body, blood was taken from an indwelling cannula at the end of each workload step, respectively. For meaningful classification of the measured quantities, blood lactate and heart rate were monitored additionally. The results for blood ammonium concentration show increasing behavior in good accordance with the established indicators for physical exhaustion, whereas sweat ammonium concentration seems to decrease with workload. This is found to be due to dilution, as sweat rate increases. The presented results provide insight in the correlation between blood and sweat parameters and therefore are of high importance for further development of wearable devices. Clinical Relevance-Sweat sensing opens up new possibilities for non-invasive, continuous in-situ monitoring of physiological parameters for healthcare and sports science applications.