The invention relates to imaging agents, and in particular to multi-modal nanoparticle (NPIA) imaging agents offering magnetic, radionuclide and fluorescent imaging capabilities to exploit the complementary advantages of magnetic resonance imaging (MRI), positron emission tomography (PET), single-photon emission computed tomography (SPECT) and optical imaging (OI). The invention extends to these new types of agents per se, and to uses of such agents in various biomedical applications, such as in therapy and in diagnosis.
