Patent ID: 7033747

Claim:
A disc system for conducting an assay on a sample, comprising; a rotatable disc with a chamber for receiving the sample; a plurality of beads in the chamber including at least two different groups of beads, each of the beads in each group having a common physical characteristic and having attached thereto at least one capture probe with affinity to a specific target; wherein said common physical characteristic of the beads of one group is different from the physical characteristic associated with the other groups; wherein said physical characteristic comprises density; and a medium in the chamber for forming a density gradient in response to rotation of the disc such that different locations in said medium have density that substantially matches the density of beads in one of said groups of beads so that rotation of the disc causes beads from the different groups to move radially within the medium to the locations where the density of the beads substantially matches the density of the medium, said beads thereby coming to rest at different locations in the chamber.