pH micro sensor with micro-fluidic liquid-junction reference electrode on-chip for cell culture applications

pH micro sensors are nowadays often realized as potentiometric sensors with a metal oxide and a reference electrode. Many used or presented potentiometric pH micro sensors clearly lack in performance due to the used reference electrode. In this work, we describe a micro reference electrode with liquid-junction on chip, which is combined with iridium oxide as pH sensing electrode. The micro-reference electrode shows a defined potential independent of the chloride ion concentration in the measurement electrolyte and a low drift rate of only 4 mV/day, which can be easily further reduced by adaption of the geometry. The micro sensor has an integrated reference electrolyte volume as liquid junction to connect the electrode element (Ag/AgCl in KCl solution) with the measurement medium. The sensor especially benefits from a simple and cost-effective production and filling process. The system is intended for usage in cell culture and drug screening applications.