The idea of using magnetic sensing for biomarker detection originated with David Baselt, a researcher at the U.S. Naval Research Laboratory. But the Stanford group's use of magnetic nanoparticles "clearly speeds up the process," says David Walt, a chemistry professor at Tufts University. In the Proceedings of the National Academy of Sciences, Wang's group describes the detection of very low levels of seven cancer markers in serum in as few as 30 minutes. "The results with serum suggest the method has promise," Walt says.

Electronics giant Philips also plans to commercialize a handheld device that uses magnetic nanoparticles next year. The device captures molecules in saliva that indicate drug use and uses magnets to bring them to a simple imager.

But Marc Porter, a chemical-engineering professor at the University of Utah, is confident that magnetoresistance will be an important tool for diagnosing complex diseases like cancer and heart disease, where more sensitive readings of multiple proteins, not just one, will lead to better diagnoses. Along with Utah researcher Michael Granger, Porter is developing a biomarker scanner that works more like a computer hard drive than does Wang's, scanning a magnetoresistant head over magnetically labeled biological samples. Porter and Granger also plan to start a company to get their scanner on the market.

Wang adds that magnetic scanners should be much less expensive than standard biomarker scanners. The instrument that reads the output of Wang's chip is smaller than the optical systems required to read fluorescent signals, and it will probably cost less than $10,000. Other researchers working on biomarker-detection systems that use microfluidics are aiming for even smaller and cheaper systems that can go out into the field. But Wang says that his system will integrate well with existing hospital infrastructure.

Wang says that MagArray is writing up an application to the U.S. Food and Drug Administration to do clinical trials of the cancer scanner in order to compare the blood-protein levels of healthy people and those with cancer. "At this point, the field of biomarkers is still under development," says Wang. "What the relative abundance of biomarkers means is not yet clear."