By measuring how much light radiates from a particular protein's spot in the bar code, Heath and Hood can quantify its concentration in the blood. Heath notes that the chip can measure blood proteins present over a wide concentration range, making it possible to measure not only plentiful blood proteins created by the immune system, but also rarer proteins originating in organs such as the brain. The device is as sensitive as conventional protein tests, and Heath and Hood can measure any proteins they're interested in by making custom chips with the right antibodies.

While other groups have focused on proteins that are created by many organs, making the results difficult to interpret, Hood says, "We're developing a strategy to identify blood proteins that are organ-specific." Hood says his group is currently using mass spectrometry to discover proteins specific to the liver and brain.

In their published paper, the researchers describe using the blood test to determine the risk level of people with breast and prostate cancer. Heath says that the chip is being tested in clinical trials involving both cancer patients and healthy individuals. The studies of healthy patients that the group is currently undertaking would be impractical using technologies that require a large blood draw, but using the chips, Heath says that it's possible to measure blood proteins several times a day. The researchers are using the blood chips to monitor how diet and exercise influence blood-protein composition.

"These devices should lead to a decrease in cost and an incredible benefit to patients," says Emil Kartalov, a professor of pathology at the University of Southern California's Keck School of Medicine. Kartalov, who's not collaborating with Heath and Hood, is developing similar chips, and he developed some of the separation methods used on the blood chip. Kartalov says that Heath and Hood's work is a major step forward, but that for these chips to truly go out into the field, they'll need to move beyond fluorescent proteins. Fluorescent microscopes are too expensive and too bulky to be carried onto the battlefield or into patients' homes. Kartalov says that future diagnostics will probably replace the fluorescent proteins with charged proteins, since measuring changes in electrical current is much simpler and more practical.