Mixing of a sample containing a suspect bioagent or antigen with 1.degree. recognition molecule coated magnetic beads in the preliminary stage of an enzyme linked immunoassay ("ELISA") procedure is emulated by first inserting the coated magnetic beads into a non-magnetic confinement region, generating a magnetic field B along the axis of said non-magnetic confinement region to agglomerate the coated magnetic beads into a porous mass; then percolating or otherwise forcing the sample solution through said porous mass; and withdrawing the magnetic field to de-agglomerate said coated magnetic beads. In seeping or otherwise flowing through the magnetic beads the molecules of the sample link to respective magnetic beads that are coated with recognition molecules.