By virtue of the unique magnetic properties and other functionalities, multifunctional magnetic nanoparticles (MNPs) are very promising in diagnostic and therapeutic applications. This review summarizes recent developments pertaining to the synthesis of MNPs with focus on the various surface modification strategies such as chemical synthesis, self-assembly, and ligand exchange. Recent applications of MNPs to multimodal imaging including magnetic resonance imaging (MRI)/optical imaging (fluorescent dyes, quantum dots (QDs), near-infrared absorption and up-conversion luminescence, MRI/positron emission tomography (PET), MRI/X-ray computed tomography (CT), and triple modality imaging are discussed. In addition, targeted drug and gene delivery, hyperthermia treatment for cancer, and other biomedical diagnosis rendered possible by MNPs are described.

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Fluorescent magnetic colloidal nanoparticles (FMCNPs) are produced by a two-step, seed emulsifier-free emulsion polymerization in the presence of oleic acid and sodium undecylenate-modified Fe3 O4 nanoparticles (NPs). The Fe3 O4 /poly(St-co-GMA) nanoparticles are first synthesized as the seed and Eu(AA)3 Phen is copolymerized with the remaining St and GMA to form the fluorescent polymer shell in the second step. The uniform core-shell structured FMCNPs with a mean diameter of 120 nm exhibit superparamagnetism with saturation magnetization of 1.92 emu/g. Red luminescence from the FMCNPs is confirmed by the salient fluorescence emission peaks of europium ions at 594 and 619 nm as well as 2-photon confocal scanning laser microscopy. The in vitro cytotoxicity test conducted using the MTT assay shows good cytocompatibility and the T2 relaxivity of the FMCNPs is 353.86 mM(-1) S(-1) suggesting its potential in magnetic resonance imaging (MRI). In vivo MRI studies based on a rat model show significantly enhanced T2 -weighted images of the liver after administration and prussian blue staining of the liver tissue slice reveals accumulation of FMCNPs in the organ. The cytocompatibility, superparamagnetism, and excellent fluorescent properties of FMCNPs make them suitable for biological imaging probes in MRI and optical imaging.

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