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

Abstract

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.