Improved Sweat Artifact Tolerance of Screen-Printed EEG Electrodes by Material Selection-Comparison of Electrochemical Properties in Artificial Sweat

The accurate diagnosis of sleep disorders requires an electroencephalography (EEG) recording. However, in-home EEG-based sleep monitoring has been hindered by the present cumbersome electrode systems which are impractical for patient self-application. To overcome this shortcoming, we recently introduced a self-applicable facial electrode set with screen-printed EEG electrodes. However, one remaining challenge in overnight EEG measurements is the presence of a low-frequency sweat artifact commonly occurring in sleep recordings. Here, the purpose was to improve the electrochemical properties of the electrodes so that they are more sweat tolerant. We selected three commercial Ag and Ag/AgCl inks (manufactured by Dupont, PPG, and ECM) for the fabrication of screen-printed electrode sets with differently shaped ink layers and compared their electrochemical properties. The open circuit potential and electrical impedance spectroscopy measurements were conducted in a custom-made electrochemical cell filled first with physiological saline and then with artificial sweat. Based on our measurements, the Ag/AgCl layer on top (i.e. in contact with the solution) mainly determines the electrochemical characteristics whereas the Ag layer underneath plays only a minor role. In artificial sweat, the ECM electrodes possessed the most satisfactory properties being very stable with the most reproducible impedance characteristics (standard deviations were significantly ($p <; 0.05$ ) lower compared to the PPG and DUPONT electrodes). This study demonstrates that the screen-printing technique is suitable for the production of highly reproducible EEG electrodes with high stability and adequate impedance characteristics. However, careful selection of ink materials is essential due to the observed differences in their electrochemical stabilities in artificial sweat.