An anonymous reader writes: Vinci Hung, a PhD candidate at University of Toronto has developed a tiny tattoo which looks like a smiley face with a hat on it. The tattoo is actually an ion-selective electrode that monitors pH levels of human skin while relating them to metabolic changes in our body. The tattoo was created using a standard screen printer, and it’s as harmless and temporary as any rub-on tattoos that you might find in a toy store.
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