Magnetic particles, such as Dynabeads™ and Pierce™ magnetic beads, have largely replaced agarose beads as the preferred support for immunoprecipitation and other micro-scale affinity purification procedures. Magnetic particles are solid and spherical, and antibody binding is limited to the surface of each bead. While they do not have the advantage of a porous center to increase the binding capacity, magnetic beads are significantly smaller than agarose beads (1 to 4 μm diameter), which collectively give them sufficient surface area for high-capacity antibody binding.