Each year, lab technicians use ion-selective electrodes (ISEs) to make more than 1 billion measurements of ion concentrations in biological and environmental samples, according to industry estimates. Those measurements, which are typically made with engineered lab instruments costing hundreds of dollars or more, might soon be made in the field with inexpensive, disposable paper-based systems.
University of Minnesota chemists Jinbo Hu, Andreas Stein, and Philippe Bühlmann have simplified ISE measurements by embedding a complete potentiometric cell into a single piece of filter paper. The low-cost system consists of printed polyurethane-based microfluidic channels to control the flow of aqueous solutions, an ion-selective membrane such as the kind used for ion exchange, a reference membrane, and stencil-printed Ag/AgCl electrodes. A simple voltmeter serves as a read out device (Angew. Chem. Int. Ed. 2016, DOI: 10.1002/anie.201603017).
The team notes that in contrast to other paper-based detectors, the new single-use device does not require careful assembly, pretreatment, or calibration. Measurements of chloride and potassium ion levels in blood serum samples show that the device yields highly reproducible results from sample volumes as small as 20 µL.