Calibration-Free Ion Sensing

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This project is funded by the Chemical Measurement and Imaging Program of the Division of Chemistry. Professor Philippe Buhlmann of the University of Minnesota - Twin Cities is developing redox buffer polymers and redox buffer nanoporous carbons to demonstrate their application for sensors. This approach extends the sensor lifetime and requires no calibration. Chemical sensors are used to measure the concentration of chemical species in water, food, industrial liquids, and biological samples in a similar way as a thermometer is used to measure temperature. In particular, electrochemical sensors with high selectivities are used for billions of measurements of ion concentrations annually. Unfortunately, conventional ion sensors must be recalibrated frequently, which requires a constant supply of reagents and either automation or trained personnel. This complicates point-of-care applications and raises cost. This work eliminates the need for recalibration. Broader impacts are also evidenced through the inclusion of high school students in the research activities and outreach activities that introduce sensors in hands-on-activies in community libraries. Polymers and nanoporous carbon materials with a redox buffer capacity at a well-defined electrochemical potential offer a unique way to prepare calibration-free sensors. The materials developed in this project exhibit features distinguishing them from previously reported polymers and carbons with redox-active groups: they exhibit batch-independent electrochemical potentials with a high reproducibility and good long-term chemical stabilities. These properties result from two design principles: (i) the redox buffer polymers and nanoporous carbons incorporate both the oxidized and reduced form of a distinct redox couple in equal quantitities, defining the potential as given by the Nernst equation. (ii) the redox-active groups are specifically selected to be stable under ambient conditions both in the oxidized and reduced form. The response mechanism of potentiometric sensors using these new materials is thoroughly investigated, which includes the quantification of electron and ion conductivities in the redox buffer polymers as well as the interfacial electron and ion transfer kinetics.