Magnetite (Fe3O4) nanoparticles (NP) are promising materials in the field of biomedical research.The use of cage-proteins, e.g.ferritin, in which the magnetic particles are formed, has proven to be a very valuable method to obtain water soluble, size-controlled superparamagnetic NP (magnetoferritin).Unfunctionalised magnetoferritin has proven to be a promising contrast agent for molecular MRI, but it is characterised by a very short circulation lifetime.