A miniaturization scheme of flexible inkjet-printed Ag/AgCl(s) reference electrodes using the ionic liquid (IL)-typed PVC membrane with the addition of graphene for electrochemical sensing applications

In this paper, we study size effects on the reference electrode performance of flexible inkjet printed electro-chemical (EC) sensors and present a scheme to print a reliable miniaturized Ag/AgCl(s) electrode for biomedical device applications. The newly printed electrode only with a size of 6900 mu m2, i.e., equivalent to 83 x 83 mu m2 can perform as well as the commercial one. Experimental results show the electrode impedance is effectively reduced via the incorporation of graphene flakes into the ionic liquid-based PVC film coated on the electrode to accelerate the ion-transferring rate of the chloride ions, thereby facilitating rapid chloride ion redistribution for the film to reach a quick potential balance with the reference electrode for open circuit potential (OCP) mea-surement. The EC sensors using the reference electrode can exhibit a fixed OCP output with a low potential variation, quick response time and potential drift, which are +/- 2.1 mV variant, 50 s, and 23.5 mu V/h, respectively regardless of the concentration of chloride ions in the tested environment.