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A Card-Swipe for Medical Tests?

by Lynn Shapiro, Writer | November 03, 2008

The new research showed the method was very sensitive, detecting as few as 800 microscopic particles that mimicked disease-related substances.

GMR's capability to detect a single particle of a biological substance "is just over the horizon," which could be used to test blood or other samples for viruses that can cause disease in minute concentrations, Porter says.

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Card-swipe testing devices would be inexpensive because they use existing, inexpensive hard-drive technology, Granger says. "The price would be such that small diagnostic labs could buy them, and eventually your local pharmacist could have one," Porter envisions.

Porter says a sample card swiped in a GMR sensor device conceivably could hold 1,900 different samples for testing, but that in most medical settings, less than a dozen tests would be needed. Nevertheless, "you eventually might test for hundreds of proteins or other compounds in the body when profiling a person's health," he says.

Turning Nobel-Winning Knowledge Into Medical Technology

The new testing method, magnetoresistance, is a phenomenon discovered independently in 1988 by Albert Fert of France and Peter Grunberg of Germany. They shared the 2007 Nobel Prize in Physics for the discovery.

Magnetoresistance is the change in a material's resistance to electrical current when an external magnetic field is applied to the material. That change usually is not more than 1 percent. But some multilayer materials display a change in resistance of as much as 80 percent. That is giant magnetoresistance.

Porter says GMR "is an ultrasensitive method to detect magnetic footprints," and is used to read data from computer hard disks and from MP3 music players.

According to the Nobel Foundation: "A hard disk stores information, such as music, in the form of microscopically small areas magnetized in different directions. The information is retrieved by a read-out head that scans the disk and registers the magnetic changes.... A read-out head based on the GMR effect can convert very small magnetic changes into differences in electrical resistance and therefore into changes in the current emitted by the read-out head. The current is the signal from the read-out head and its different strengths represent ones and zeros."

In the first new study, Porter, Granger and colleagues set the stage for using GMR devices to test medical, environmental or other biological samples.

The prototype reader had four GMR devices: two sensors to detect changes to the magnetic fields of the sample spots, and two "reference elements" to distinguish how magnetic measurements were affected by temperature changes as opposed to the presence of disease indicators in medical samples.