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 electrochemical (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 μm², i.e., equivalent to 83 × 83 μm² 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) measurement. 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 μV/h, respectively regardless of the concentration of chloride ions in the tested environment.