Patent ID: 8343777

Claim:
A method to detect the presence of a magnetic bead, comprising: providing an assemblage of micro-structures; at a first temperature, adding a magnetic micro-bead to said assemblage of micro-structures thereby attaching said micro-bead to a binding site of said micro-structures; providing a detector that signals the presence of a magnetic field through a change in electrical resistance of a free layer, that is parallel to an upper surface of said detector; at a second temperature, that is lower than said first temperature, causing said free layer to be magnetized in a bias direction; providing a static magnetic field, having a value, in a direction relative to said upper surface; providing an alternating magnetic field having a frequency, a first amplitude, and a direction parallel to said upper surface; and at said second temperature, varying said frequency and said static field value until ferromagnetic resonance (FMR) occurs, whereby said magnetic micro-bead emits a magnetic field that rotates at said FMR frequency at a second amplitude, thereby causing said detector signal to peak, at a level greater than would have occurred at said first temperature, and thereby detecting said magnetic bead.