At the University of Utah scientists are developing a machine that can identify a number of pathogens in a given sample, using a phenomenon called giant magnetoresistance. The researchers believe the technology can be made both accurate and small enough to resemble a credit card reader.
The following is from the University of Utah statement:
The new testing method makes use of "giant magnetoresistance," or GMR, a phenomenon discovered independently in 1988 by Albert Fert of France and Peter Grünberg 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.
In the first new study, Porter [Marc Porter, Utah Science, Technology and Research (USTAR) professor of chemistry, chemical engineering and bioengineering], Granger [Michael Granger, USTAR research scientist] 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.
The prototype does not yet look like a credit card reader or card-swipe device. Instead, it is used to "read" a Pyrex glass sample stick about three-quarters-inch long and one-eighth-inch wide. Biological samples can be placed on the sample stick, which then is "scanned much like a credit card reader," Porter says.
In the first study, instead of holding blood or other medical samples, the sample stick had 15 raised spots of iron-nickel "permalloy," a magnetic material that produces a magnetic signature read by GMR sensors.
The study determined how measurements by the GMR sensors – the heart of a future card-swipe device – can be calibrated to account for variations in the size of the permalloy spots, the amount of separation between the sensors and the sample stick, and on the angle of the sample stick as it is scanned by the sensors.
Those factors determine how consistently and accurately a card-swipe device would detect minute amounts of substances associated with diseases.
In the second study, the sample stick’s alloy spots were replaced by the material that would be used on real medical test cards: microscopic spots or "addresses" of gold that were no longer than the smallest known bacterium. The widths were varied to test which size of addresses could be "read" most accurately.
A substance named biotin or vitamin B-7 was bound chemically to the gold spots on the sample stick. Tiny drops of magnetic particles coated with streptavidin – a protein found in eggs – were placed on the gold spots.
"The gold address has no magnetic signature," Granger says. "Once the particles are bound to it, GMR picks up that magnetic signature. It’s a proof of principle."
The experiment was repeated hundreds of times with different concentrations of magnetic particles bound to the biological substance.
"We could detect as few as 800 magnetic particles on an address," Porter says. "We believe that with further development, we can get down to single-particle detection."
Full story: A Card-Swipe for Medical Tests
Image: This green circuit board contains giant magnetoresistance (GMR) sensors (one sensor shown in expanded view) like those that “read” data on a computer hard drive. In a testing method demonstrated by University of Utah scientists, the board would serve as the heart of card-reader that would be used for medical or environmental tests. A credit card-like sample stick containing, blood, saliva, water or other liquids would be swiped through the reader, producing electrical currents that could indicate if any of the samples contained pollutants or substances associated with various diseases. Photo Credit: Michael Granger
