Reduced graphene oxide-based electrical circuit trace on flexible cotton fabric

Electrocardiography (ECG) is one of the methods used for monitoring the heart condition. There are increasing demands for the development of wearable and flexible ECG systems to be implemented for long term ECG monitoring. In the development of wearable circuits, polymer material has been widely used to enable the flexibility properties. However, polymer may cause allergy to human skin, and the inability of the polymer to pass through moisture at human skin makes it inappropriate to be used for wearable applications. Cotton fabric is an alternative substrate for the polymer since it is natural, hypoallergenic and able to pass through moisture of human skin. Thus, the objectives of this research were focused on designing and fabricating traces of ECG circuit on cotton fabric; investigating the effects of mechanical characterization on the conductive line; and validating the ECG signal acquisition using the fabricated circuit trace with 0.2 % w/w of graphene oxide ink was used as the conductive material. The fabrication process of conductive line on cotton fabric includes the production of wax impregnated paper, wax transferred from wax impregnated paper onto cotton fabric, pipetting of graphene oxide ink onto the cotton fabric, and reduction of graphene oxide. The resistance of 1.97 kQ was produced in 1 mm wide and 20 mm long conductive line coated with 30 layers of graphene oxide. Two mechanical characterizations were performed on the conductive line; washing and folding tests. In washing test, three solutions were used including distilled water with pH = 7, detergent solutions with pH = 8 and pH = 9. The conductive line remained 84 % after fifth times of washing using distilled water with pH = 7. In folding test, the conductive pattern remained 73 % after tenth times of -180 ° and 180 ° angles of folding. During ECG signal acquisition using cotton fabric-based circuit trace, the features of ECG signal are successfully acquired and displayed. However, there is a 60 Hz electrical noise included in the signal due to the capacitive component in the cotton fabric-based circuit trace. This research acts as a preliminary phase in developing a flexible and fully functional cotton fabric-based ECG monitoring system which can be used for long term ECG monitoring

Optimization of reduced GO-Based cotton electrodes for wearable electrocardiography

The quality of Electrocardiography (ECG) signal is dependent on the electrode's performance. Comfort and long-term monitoring are the main benefits of a dry and flexible electrode compared to conventional silver/silver chloride (Ag/AgCl) electrode. The main objective of this study is to develop high performance textile-based electrode by optimising fabrication method and electrode design. Cotton fabric was dipped into graphene oxide (GO), followed by reduction process to form reduced graphene oxide-cotton (rGOC), where L-ascorbic acid (C6H8O6) was used as the reducing agent. Conductivity and skin-electrode interface impedance of the fabricated cotton were characterized using Four-point probe (Van der Pauw) and Potentiostat, respectively. This study focuses on the investigation of electrode design that includes fabrication methods, electrode sizes and shapes. The performance of the reduced GO-based cotton (rGOC) electrode in terms of ECG signal quality was compared to conventional Ag/AgCl electrode and metal clamp under static and dynamic wearable conditions. Results from the conducted experiments show that the fabricated electrode's performance is influenced by dipping time and electrode design, with circle-shape electrode shows the highest conductivity (up to 9k S/m at 1 cm2 area) compared to square- and rectangular-shape electrodes (<8k S/m and 14.55 S/m, respectively, at 1 cm2 area). The circle-shape rGOC electrode's performed better (SNR 14.85±0.22 dB) than Ag/AgCl electrode (SNR 11.26±0.18 dB) and metal clamp (SNR 12.28±0.72 dB) in capturing static ECG signal. A wearable circle rGOC electrode with 1.7 cm radius performed also similarly under static (SNR 32.60±0.72 dB) and dynamic (SNR 30.27±1.37 dB) ECG monitoring, respectively