Polypyrrole (PPy) conductive polymer coating of dry patterned vertical CNT (pvCNT) electrode to improve mechanical stability

Traditional wet or gel electrodes are not suitable for long duration neuro-physiological monitoring. Dry electrodes for impedimetric sensing of physiological parameters (such as ECG, EEG, and GSR) promise the ability for long duration monitoring. We have previously demonstrated a novel nanotechnology based dry electrode configuration fabricated with patterned vertically-aligned carbon nanotube (pvCNT) for neuro-physiological impedimetric measurements. However, the fabricated sensors were mechanically weakly adhered to the substrate. This paper describes a coating mechanism of pvCNT with a thin layer of conductive polymer, Polypyrrole (PPy), to increase mechanical stability, while preserving superior impedance properties of pvCNT. The electrodes were fabricated on circular stainless-steel (SS) foil substrate (φ = 10 mm, and thickness = 2 mils). Electrically conductive multi-walled CNT were grown in pattered pillar formation with a square base of 100 μm each side, and an inter-pillar spacing of 200 μm. The heights of the pillars were between 1 to 1.5 mm. The coating procedure involved applying 10 μL of PPy after preparing the pvCNT with 70% ethyl alcohol solution, and flash drying at 300°C. A comparative test with commercial ECG electrodes and non-coated version show that coated pvCNT has lower electrical impedance compared to commercial electrode whereas higher impedance compared to non-coated version. The signal capture were comparable for all electrodes in vitro. The peel test reveal much stronger mechanical adhesion of the pvCNT with the SS substrate when coated with PPy. The results demonstrate the feasibility of coating pvCNT dry electrodes with PPy for robustness.