Fabrication and characterization of transparent and flexible CNT–PDMS micro-column electrode for electrocardiogram monitoring

Recently, with the rapid growth of wearable healthcare devices, there has been an increasing demand for transparent and flexible electrode technologies that can adhere stably to curved and irregular surfaces while maintaining signal stability during long-term measurements. In this study, we propose a transparent and flexible CNT–PDMS based micro-column electrode that incorporates microscale protrusions to enable multi-point contact, thereby reducing contact impedance and enhancing signal stability. The proposed electrode features a continuous monolithic structure integrating an upper micro-column layer with a lower grid framework, which expands the effective contact area and uniformly distributes contact pressure on curved surfaces. CNT content optimization experiments (5–25 wt%) confirmed that a stable conductive pathway was established at 20 wt%, which was selected as the final composition. ECG signal quality was comparatively evaluated under identical conditions using commercial Ag/AgCl electrodes (gel removed), sheet-type electrodes, and micro-column electrodes with diameters of 480 μm, 690 μm, and 1,020 μm. The 690 μm micro-column electrode exhibited the best performance, with RMS 0.75% higher and SNR 4.7 dB greater than the commercial Ag/AgCl electrode. These results demonstrate that stable ECG signal acquisition can be achieved without conductive gel in both initial and long-term measurements, highlighting the electrode’s high applicability in curved-surface environments, wearable devices, and in-vehicle biosignal monitoring applications.