COMPEL™ are highly uniform superparamagnetic microspheres ideal for applications that demand uniform particle response, such as miniaturized bioassays and separations. COMPEL™ are comprised of iron oxide crystals dispersed in a polymer matrix, with a functional polymer overcoating for the encapsulation of magnetite and the introduction of reactive groups. As they are polymer-based, they retain the low density that is advantageous for biomolecular assays. Our initial offerings include 3μm, 6μm, and 8μm beads with measured CVs of 5% and high levels of COOH-functionalization. The carboxyl-modified undyed COMPEL are supplied as ~5% solids (w/w) and the fluorescent and streptavidin-coated versions of COMPEL are supplied at ~1% solids (w/v).: