A composition and methods of use and preparation are provided. The composition may comprise a magnetic nanoparticle comprising: a passivation layer; and at least one unique entity that is attached to the magnetic nanoparticle. For example, the composition may include a magnetic nanoparticle and an antibody attached to the magnetic nanoparticle. Such magnetic nanoparticle architecture can provide treatment by, and screening of, nanoparticles functionalized with various functional species.