A Self-Wetting Paper Electrode for Ubiquitous Bio-Potential Monitoring

This paper aims to develop a flexible and cost-effective dry electrode with low and stable contact impedance. With these benefits, the electrode can be practically used in ubiquitous bio-potential monitoring with similar signal-to-noise ratio as commercial wet electrode. A self-wetting electrode is developed by the aid of moisture naturally created by skin under the electrode. It consists of a layer of ethylcellulose fiber paper coated with PEDOT/PSS (PCwPEDOT) and a thin layer of parylene. PCwPEOT, which has a large contact area composed of micro-scale fibers, is a 30- $\mu \text{m}$ flexible membrane that acts as the electrode material. A 3- $\mu \text{m}$ parylene bonding at the backside of PCwPEOT, as a high-performance vacuum membrane, can collect moisture or sweat naturally evaporating from the skin and store it in the PCwPEDOT layer. This design increases the humidity of skin, especially the water content in the corneum, acting as electrolyte containing ions, increases effective contact area between electrode and skin, and decreases the impedance of the electrode. With an environmentally friendly and cost-effective fabrication process, the 33- $\mu \text{m}$ thickness of electrode is light and flexible. It can be tailored to proper size according to the application. It achieves lower contact impedance compared with dry electrodes with a similar structure. Its recording performance is comparable to commercial patch electrode. The proposed electrode provides high-quality signals, and comfortable user experience in bio-potential recording. It is feasible for developing a long-term wearable system for bio-potential monitoring.