Determination of the selectivity of printed wearable sweat sensors

The characterization and system integration of a fully screen-printed electrolyte biosensor is described. The purpose of this sensor is to determine the state of fitness during sports activity by measuring the ammonium concentration in sweat. Focusing on the selectivity of the ammonium sensor against interfering sodium and potassium ions, the separate solution method (SSM) and the fixed interference method (FIM) are compared on the basis of a single sensing device. The latter is mainly supported by the excellent stability of the sensors. For both interfering ions, the FIM analysis shows a sufficient margin for the operation of the sensor in the desired application in wearable health and fitness monitoring from sweat. The selectivity coefficients are better than 0.01 for sodium and still better than 0.1 for potassium. SSM delivers higher selectivity in both cases, although the discrepancies in selectivity point towards further optimization potential in the sensor architecture or materials combination.