Inkjet-Printed Planar Silver/Silver Chloride Pseudo Reference Electrode for Microfluidic Potentiometric Sensor Applications

The miniaturization of electrochemical sensors for potentiometric measurements can be made possible using microfabrication technologies. However, conventional reference electrodes (RFs) are often challenging to miniaturize and integrate, limiting the compactness of the microfluidic setup for potentiometric sensors. In this study, we have developed a method for inkjet printing planar solid-state Ag/AgCl pseudo REs on a TiW-Au coated Si-based potentiometry sensor. A method for inkjet printing of pseudo REs was established for two sensor variants: planar sensors and sensors with an integrated microfluidic cell. The pseudo RE in both sensor versions showed stable potentiometric readings for 70 days with a standard deviation below 1 mV. Sensor potential readings using the pseudo RE and conventional RE were comparable, showing linearity and near Nernstian response. However, the sensors with the pseudo RE showed to be less robust compared to commercial screen-printed electrodes (SPEs), lasting fewer calibration cycles. Inkjet printing provides a straightforward and cost-effective method for the incorporation of pseudo REs into miniaturized potentiometric sensors. This approach is compatible with post-processing steps following microfabrication, aiming to facilitate the development of monolithically integrated microfluidic sensors for automated on-site analysis.