These temporary tattoos measure glucose

This gel pen creates temporary tattoos that act as chemical sensors.

At the local office supply store, a roller-ball gel pen will cost you about 50 cents. With a little tinkering, researchers are taking that same pen and using it to measure glucose levels.

Nano-engineers at the University of California, San Diego have invented a technique that turns cheap pens into dispensers for do-it-yourself sensors. They replace the regular gel with a custom biochemical ink that can measure specific chemicals.

When drawn on the body, the ink adheres much like a temporary tattoo. It can detect things like the amounts of sodium insulate, lactate and glucose in your sweat. To read the measurements, the group is creating an electric Bluetooth-enabled device that will take the info from the drawn-on sensor and transfer it to a smartphone or laptop.

For diabetics who need to check their blood glucose levels daily, this could be a cheaper alternative to prefabricated glucose strips. (Earlier this year, another group of researchers tested a temporary paper tattoo that measured glucose levels using a small electrical shock.)

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Currently, the drawings can only provide a single measurement, but the researchers would like to eventually make a single tattoo work for all-day monitoring. The pen encourages creative doodling, which could be appealing for children.

"The whole point was having a system that can be used easily by any untrained end users to develop sensors by themselves," said Amay Bandodkar, a fourth year graduate student at UC San Diego who created the pen. The work was led by professor Joseph Wang in the Department of NanoEngineering.

The applications aren't limited to the human body. To measure toxins in the air, such as phenol, the group drew on the leaves of plants. The ink isn't toxic and doesn't hurt the foliage.

Though they are still in the early stages of developing the technology, the researchers are looking into expanding the number of chemicals the pen can detect.

Bandokar thinks the technology, called enzymatic sensors, could serve a wide range of real world uses. For example, a soldier could draw a line on a wall to detect explosives or gunshot residue. In some situations, the drawing could blend into its surroundings without arousing suspicion.

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