Detection of pH and Sodium using Textile-based Ionophore-doped Ion-Selective Electrodes (ISEs)

Conventional ISEs with sensing membranes containing liquid contacts give the expected Nernstian responses with low limits of detection. However, when they are converted to a miniaturized planar design, they give sub-Nernstian responses with a narrow detection range and poor reproducibility. Point-of-care devices have recently increased interest because they are low-cost, simple to use, portable, and only require a small sample. Currently, there are only a very limited number of ISE systems with ionophores fully integrated into paper or textiles that are sensitive to potassium. For other ions, attempts to integrate ionophore-doped sensing membranes in paper or textiles, the devices do not give the selectivity expected from the ionophores.

To investigate the membrane–substrate system, studies were performed using UV-Vis, NMR, and LC-MS to analyze if any compounds leached from the textile substrate that would interfere with the sensing membrane. A parallel experimental design to the planar devices was devised and optimized to confirm that the sensing membrane is compatible with the substrate. The use of a sealant to seal the sensing membrane from the environment, preventing the formation of a leakage path formed by a thin water layer, allows the devices to have a Nernstian response for pH and sodium, thus far. Although the reproducibility of each measurement needs to be improved upon, the optimization of this approach is critical to the successful development of miniaturized ionophore-doped ISEs of low cost, as needed for applications in resource-limited environments.