The present invention provides nanoparticles having a core comprising a magnetic material and having a surface, where the surface may be operatively linked to an antigenic peptide-major histocompatibility complex (MHC) monomer. The antigenic peptide-MHC monomer may then be recognized by a T cell receptor. These nanoparticles may further comprise a signal-generating label, such as a fluorophore. Methods employing nanoparticles of the present invention may involve magnetic resonance imaging and/or fluorescence detection, such that cell imaging and localization are performed.
