Ion-selective electrodes with ionophore-doped sensing membranes are are highly sensitive and selective analytical tools that offer a variety of advantages, such as simplicity of measurement, high analysis throughput, rapid detection, and low cost of analysis. While such sensors are used in clinical laboratories for billions of measurements every year, applications in biomedical sciences, the food industry, and environmental monitoring are hindered by biofouling and the frequent need for recalibration. With prolonged exposure to biological samples, solid contact polymeric-membrane ISEs exhibit a breakdown of selectivity and response due to biofouling and changes in the phase boundary potential at the interface of the ion-selective membrane and the underlying electron conductor. Therefore, frequent recalibrations are needed for many clinical and biological applications. This talk will discuss experimental techniques such as impedance spectroscopy and hydrodynamic methods to characterize sensor aging, and it will address the use of hydrophobic redox buffers incorporated into the sensing membranes to stabilize the phase boundary potential at the interface to the underlying electron conductor. These redox buffers permit a high electrode-to-electrode reproducibility of the emf response, which is needed for the development of ion-selective potentiometric devices that can be used in a calibration-free manner [1].

[1] Calibration-Free Ionophore-Based Ion-Selective Electrodes With a Co(II)/Co(III) Redox Couple-Based Solid Contact, Zou, X. U.; Zhen, X. V.; Cheong, J. H.; Bühlmann, P. Anal. Chem., 2014, 86, 8687–8692.