Machine Design

Magnetic biochip

Giant Magnetoresistive (GMR) materials vary electrical resistance according to changes in an applied magnetic field.

The interaction generates electrical signals that can be read as data. Stanford researchers used this principle to build GMR sensor arrays for DNA analysis.

They first immobilized single-strand DNA receptors on the surface of a GMR sensor array. They then captured oligonucleotides with genetic sequences of interest. Oligonucleotides are structural units of DNA. Streptavidin is a protein that binds to biotin molecules, which oligonucleotides contain. The idea is to coat magnetic nanoparticles with streptavidin and let them bond to the biotin. Once that happens, the GMR sensor picks up changes in the magnetic field, which are converted into a unique electrical signature associated with each oligonucleotide under study.

The Stanford work is said to be the first to use a sensor array with this technique. The array contains more than 1,000 sensing elements within 1 mm2. It is integrated with 0.25- m BiCMOS circuitry on a chip. Such GMR sensor arrays may make feasible low-cost, portable diagnostic instruments, and ultimately compete with more complex and costly optical-based systems.

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