Microfluidic Reference Electrode with Free-Diffusion Liquid Junction

The accuracy of many biological and chemical sensors is critically dependent on the stability of the potential imposed or sensed through a reference electrode. As these sensors are miniaturized, the reference electrode has to be miniaturized simultaneously without any loss to its stability. In this paper, we describe a new microfluidic miniaturized silver/silver chloride reference electrode that demonstrates significantly better stability and lifetime than conventional designs. In our new design, we have miniaturized the existing format of the macroscale reference electrode and added the capability to replenish the internal solution by integrating it with a microfluidic channel. The replenishment of the internal solution significantly improves the performance of these electrodes over other miniaturized designs. We demonstrate reference electrodes that are very stable (potential variation of <0.1 mV), with minimal drift (∼1 mV) and lifetimes longer than 100 hours. We have also characterized the behavior of these electrodes to changes in pH and chlorine concentration of the external solution. The results indicate insensitivity of the microfluidic reference electrode potential to the presence of any analyte in the test solution.