The last few years have witnessed the development of magnetoresistive chips for use in biological assays 1, 2. In these assays, target biomolecules are labelled with nano- or micrometer-sized magnetic particles and are recognized by biomolecular probes immobilized over sensing sites. The detection of biomolecular recognition between probes and targets (e.g. DNA hybridization or antibody-antigen interaction) is accomplished by sensing the stray magnetic fields created by the labels using magnetoresistive sensors. These transducers change their electrical resistance in the presence of a magnetic field and are typically used in read-heads of hard-disk drives.
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