You’ll find the design of this prototype skin sensor out of University of California, San Diego either endearingly goofy or just scary. This paper ‘tattoo’ is actually a solid-contact ion-selective electrode (ISE) made using standard screen printing techniques finished with an electropolymerization process on commercially available transfer tattoo paper. The two ‘eyes’ are actually electrodes which measure perspiration on the skin’s surface to determine stress-related changes in pH and clues to metabolic diseases such as Addison’s, or more simply fatigue or dehydration. The tattoo sticks to even wet skin. It can also measure sodium, potassium and magnesium with different sensing materials. There’s great potential for this not only in sports, but also in assisted living and rehabs where one of the most serious conditions is gradual, invisible dehydration of residents. Tattoo-based medical sensor puts a happy face on detecting metabolic problems (GizMag) Happy face tattoo does serious work (University of Toronto release)