International audienceUse of paramagnetic particles to isolate molecules or cells from complex media is well established. Typically, particles are manufactured and coated with a biological molecule which confers specific biorecognition. Incubation of particles with sample and exposure to magnetic fields isolates the species of interest. We designed, produced and assessed magnetized fusion proteins consisting of the antigen binding portion of an antibody (single chain Fv; scFv) fused to the heavy chain of the iron binding protein ferritin. The fusion protein subunits expressed in E. coli assemble to form a fusion protein consisting of a ferritin sphere with scFvs on the surface. The fusion proteins were chemically magnetized by introducing a paramagnetic iron core. The resultant fusion protein was shown to be magnetizable as well as capable of binding target antigens. These “organic” magnetizable particles possess a number of theoretical advantages over traditional inorganic particles