Multiplex Pulsed Current Sensors for Anion Detection

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Low-cost and stable sensors are needed for long-duration monitoring of nitrate and phosphate in waterways to help improve farming practices and understand the negative environmental and economic impacts caused by the release of these ions. One established platform that shows promise for detecting these ions is the use of solid-contact ion selective electrodes (SC−ISEs). Conventional SC-ISE measurements monitor electrode potential under open circuit conditions to quantify the amount of one target analyte. These conventional SC-ISEs rely on highly engineered membrane materials that are formulated to selectively bind to the target ion. These engineered membrane materials can achieve high selectivity for nitrate and phosphate, but are vulnerable to certain interferents, require frequent calibration, and have poor long-term stability. In recent work, we demonstrated the use of pulsed current technique for anion detection in SC-ISEs, which allows for anion detection based on differences in anion diffusion through the membrane rather than selective anion binding – opening up a wide range of materials as candidates for ion sensing membranes. In this report, we employ pulsed current measurement to examine anion detection using three common polymers as membrane layers: polyvinyl acetate (PVA), polyvinylchloride (PVC), and polyacrylonitrile (PAN). We measure the potential vs. time response for these three membrane materials in solutions containing various anions such as nitrate, phosphate, chloride, and carbonate at varying pulse currents. Afterwards, we employ tree-based and neural-based machine learning algorithms to examine the feasibility of detecting multiple ions simultaneously using the combined response data from multiple electrodes. Our experiments illustrate that our method for anion detection, used with machine learning analysis, is useful for investigating the interaction mechanisms of anions with the polymer matrix.