A new system for detecting cancer proteins uses the same magnetic phenomenon that lets computer hard drives read and write data. The Stanford University researchers developing the system hope that it will detect cancer in its earlier stages, when it's easier to treat. MagArray, a startup in Sunnyvale, CA, will commercialize the technology.

Well before cancers are visible on medical imaging scans, their cells release small amounts of telltale proteins into the blood. Researchers are developing ways to detect those proteins, frequently by tagging them with fluorescent labels. But while all biological samples have some background fluorescence, they have virtually no magnetic background. Magnetic protein detection could thus yield a clearer signal, says Shan Wang, a professor of materials science and engineering and electrical engineering at Stanford University.

Another approach to early cancer detection involves devices that catch cancer proteins on the tips of vibrating nanostructures and measure how they affect the flow of electrical current. But since the Stanford device exploits a physical phenomenon that is already the basis for consumer electronics, it could prove easier to mass-produce. "This is one of the things that will make this technology a success: there's no need to prove manufacturability," Wang says. "The challenge is to combine it with biochemistry."

Wang's device takes advantage of giant magnetoresistance, a phenomenon that won its discoverers the 2007 Nobel Prize in physics. The device is built on a silicon chip arrayed with 64 magnetic sensors called spin valves. Each valve is coated with a different kind of antibody, a molecule primed to latch on to a particular cancer protein. When the chip is exposed to blood serum, the target proteins stick to the antibodies. Wang then adds a solution of magnetic nanoparticles, also attached to antibodies, that stick to the captured proteins. The magnetic field of the captured nanoparticles measurably changes the resistance of the underlying spin valve, allowing Wang to determine the concentration of cancer proteins in the serum.

In tests where the Stanford prototype scanned for cancer proteins, including a marker of colon cancer, it was two orders of magnitude more sensitive than the standard technique for detecting blood proteins, which uses a similar antibody capture sandwich in combination with fluorescent tags.