Researchers at two startup companies and the University of Illinois are building all the capabilities of expensive lab-bench tests onto a piece of paper, without adding significant weight or other cost to the tests.

The group behind these flexible arrays of LEDs, light detectors, and transistors is also working with medical-device companies to incorporate them into surgical tools and bedside monitors for hospitals.

The company has patterned postage-stamp-sized pieces of paper with channels that wick blood and other fluids into an area treated with chemicals that change color to indicate, for example, elevated liver enzymes that reveal an AIDS patient is on the wrong drugs. The simple color-change reaction can provide critical information that lets doctors know whether a patient is in danger.