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This smiley face tattoo is monitoring you

Researchers are disguising a medical sensor that can track physical exertion levels as a temporary, smiley face tattoo.

A Ph.D. student at the University of Toronto is using the same transfer paper currently affixing temporary tattoos to kids -- in conjunction with a common screen-printing technique -- to develop a medical sensor that keeps tabs on a person's exertion by monitoring the skin's pH levels.

The eyes serve as the electrodes and the ears as the contact points for a measuring device to connect to. University of Toronto

Similar devices, which are called ion-selective electrodes (ISEs), are already common among athletic trainers and medical researchers to help spot fatigue, dehydration, or even metabolic diseases. But they tend to be bulky and don't stick well to sweaty skin.

The new sensor stays put and doesn't look so, well, medical.

"We wanted a design that could conceal the electrodes," Vinci Hung, the analytical chemistry Ph.D. candidate who helped create the new sensor, said in a university news release. "We also wanted to showcase the variety of designs that can be accomplished with this fabrication technique."

As they report in Analyst, the Royal Society of Chemistry journal, Hung and her team laid down different sensing materials, including silver and carbon fiber-modified carbon and insulator inks, to detect various components of sweat, such as sodium, potassium, and magnesium.

The eyes on the smiley face serve as the electrodes, while the ears are the contact points for a measuring device to connect to. The sensor was applied to the skin much like other temporary tattoos, including using a paper towel soaked in warm water to remove the base.

No word yet on future development or cost, and one could presumably develop such a sensor in the shape of, say, a sports team's logo. But in the meantime, if you see your favorite athlete with a smiling blue man on his or her arm, don't assume it's a fashion statement.

Correction at 8:30 a.m. PT December 5: Vinci Hung's field of study has been corrected. She is a Ph.D. candidate in analytical chemistry.