Patent ID: 8227261

Claim:
A method comprising: flowing a sample including a plurality of magnetic particles and an analyte through a fluid chamber including a detection surface comprising a resonant acoustic device having a vibrating membrane and a first capture agent linked to the detection surface, wherein the sample includes at least one magnetic particle functionalized with a second capture agent capable of binding the analyte; binding, while flowing the sample through the fluid chamber, a first portion of the plurality of the magnetic particles to the detection surface by linking of the second capture agent to the analyte to the first capture agent; applying, while flowing the sample through the fluid chamber, a magnetic field to the fluid chamber to associate a second portion of the plurality of magnetic particles with the detection surface, wherein the second portion of the plurality of magnetic particles are not linked to the detection surface by the analyte; measuring a first signal corresponding to a total amount of the plurality of the magnetic particles bound to the detection surface or associated with the detection surface during a first period of time to establish a normalized exposure; changing an amount of the magnetic field applied to the plurality of the magnetic particles during a second period of time relative to the magnetic field applied during the first period, the change in the amount of the magnetic field sufficient to cause at least a portion of the second portion of the plurality of magnetic particles to dissociate from the detection surface of the resonant acoustic device while the first portion of the plurality of the magnetic particles remain affixed to the detection surface by linking of the second capture agent to the analyte to the first capture agent; measuring a second signal during the second period of time; and comparing the first signal to the second signal to determine a change in the amount of the plurality of magnetic particles bound to the surface relative to the normalized exposure.