Iontophoresis and Ion-Selective Electrodes

Skin conductivity varies with the phases of the menstrual cycle. The first approach that we considered used iontophoresis and ion-selective electrodes to track skin conductivity. While we didn’t use this approach in our final design (click here to skip to our final design), I still think it was really interesting, so I’ll briefly cover it here. I’d recommend reading Cystic Fibrosis and Glucose Monitoring using a Fully Integrated Wearable Platform by Emaminejad et al. in 2017 to learn more. Iontophoresis is a method of transdermal drug delivery. It’s used a lot in eye medication because it’s not painful. We wanted to use it to generate sweat and then use ion-selective electrodes to analyze that sweat. Iontophoresis uses an electric current between two metal plates on the skin (see image to right). The plates are oppositely charged, and one plate has a similarly charged medication on it (for our project this would be a sweat stimulant). When the plates are turned on, the like charges of the plate and medication repel and the medication is attracted to the oppositely charged plate, traveling through the skin. As it travels through the skin, the medication is administered. At this phase, the sweat generation would be done and the sweat would be collected by either gauze or hydrogel. After that, we would analyze the sweat using ion-selective electrodes. We would need one reference electrode for sodium, one for chloride, and a shared reference. The paper by Emaminejad et al. does a really good job of explaining how they made these electrodes, so I’d recommend reading that if you’re interested in a more in-depth explanation. Ion-selective electrodes are commonly used in laboratories to test for the concentration of a specific ion in a solution. Here, by testing for sodium and chloride, we can find skin conductance and compare it to previous data.