Paper is ­easily incinerated, making it easy to safely dispose of used tests. And while paper-based diagnostics (such as pregnancy tests) already exist, Whitesides­'s device has an important advantage: a single square can perform many reactions, giving it the potential to diagnose a range of conditions. Meanwhile, its small size means that blood tests require only a tiny sample, allowing a user to simply prick a finger.

Currently, Whitesides is developing a test to diagnose liver failure, which is indicated by elevated levels of certain enzymes in blood. In countries with advanced health care, people who take certain medications undergo regular blood tests to screen for liver problems that the drugs can cause. But people without consistent access to health care do not have that luxury; a paper-based test could give them the same safety margin. ­Whitesides also wants to develop tests for infectious diseases such as tuberculosis.

To disseminate the technology, ­Whitesides cofounded the nonprofit Diagnostics for All in Brookline, MA, in 2007. It plans to deploy the liver function tests in an African country around the end of this year. The team hopes that eventually, people with little medical training can administer the tests and photograph the results with a cell phone. Whitesides envisions a center where technicians and doctors can evaluate the images and send back treatment recommendations.

"This is one of the most deployable devices I have seen," says Albert Folch, an associate professor of bioengineering at the University of Washington, who works with microfluidics. "What is so incredibly clever is that they were able to create photoresist structures embedded inside paper. At the same time, the porosity of the paper acts as the cheapest pump on the planet."

Recently, the Harvard researchers have made the paper chips into a three-­dimensional diagnostic device by layering them with punctured pieces of waterproof tape. A drop of liquid can move across channels and into wells on the first sheet, diffuse down through the holes in the tape, and react in test wells on the second paper layer. The ability to perform many more tests and even carry out two-step reactions with a single sample will enable the device to detect diseases (like malaria or HIV) that require more complicated assays, such as those that use antibodies. Results appear after five minutes to half an hour, depending on the test.

The researchers hope the advanced version of the test can eventually be mass produced using the same printing tech­nology that churns out newspapers. Cost for the materials should be three to five cents. At that price, says Folch, the tests "will have a big impact on health care in areas where transportation and energy access is difficult."

See the 10 Emerging Technologies of 2009.