By counting how many microwells light up, Walt can determine the concentration of a protein in a blood sample. In an unpublished proof-of-principle experiment, Walt says that his optical-fiber method was able to detect a human cancer biomarker in cow's blood at concentrations 250 times lower than that possible using clinical techniques.

So little is known about the 800 or more remaining blood proteins that fall under current detection limits that scientists can only speculate on their clinical relevance. "We're talking to clinicians to figure out what makes sense to test for," says Walt. Once the company picks target proteins, they'll draw on blood samples archived at hospitals and try to correlate protein levels with clinical outcomes. "Every time a more sensitive technology has become available, it has opened up new diagnostics and led to advances in treatment," says Walt.

Early detection can have a downside. "We don't want to scare people by telling them, 'You have an early tumor,'" says Walt. "It may be that the immune system takes care of small tumors." So any potential biomarkers will have to be carefully validated. But even if the new method only leads to a test for a single cancer biomarker, Walt hopes that it will improve survival rates for a large number of people.

"We believe this has the potential for transforming diagnostics," Walt says.