Using cheap materials that anyone can order by mail, scientists built several color-changing electronic displays on sheets of ordinary paper.

The device relies upon thermochromic ink, the same stuff that can be found in mood rings and disposable thermometers. When its temperature changes, so does its color.

"At first, paper may not sound like exciting, state-of-the-art stuff, but it is in fact, a very interesting material," said electrical engineer Adam Siegel, a Harvard graduate student who led the project.

Siegel works in George Whitesides' lab at Harvard, which has been churning out all sorts of inexpensive devices that could be used in the developing world. In the past years, they have also whipped up centrifuges with egg beaters and built two-cent medical tests with paper and tape.

"The goal here is to get people to think outside the silicon box," says Siegel. "That is, to think that simple, everyday materials like paper can be used in very technologically-sophisticated ways."

The inspiration for the project came from an educational science catalog that had a special ink that turns color at different temperatures.

"I thought it might be possible to pattern this ink on one side of a sheet of paper and then use electrical current to heat the paper and 'write' a message on the other side in plain English, or another language for that matter," Siegel said.

By coating one side of the paper with ink, and affixing metal heating elements to the other, Siegel built a makeshift monitor. These simple devices could provide the readout for equally inexpensive tests that can tell if someone has an infection, or if water is safe to drink, he said.

These displays may not show up in Best Buy anytime soon, but they could turn up at the Maker Faire. You can find complete instructions for building them at the Lab on a Chip website.

Citation: Thin, lightweight, foldable thermochromic displays on paper. Adam C. Siegel, Scott T. Phillips, Benjamin J. Wiley and George M. Whitesides, Lab on a Chip, 2009.

Images: Adam Siegel

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