Magnetic nanocrystals, as the core material of a new type of magnetic resonance contrast agent, have presented great potentials in early detection and treatment of diseases, especially for cancer. Following on from our previous investigations on Fe₃O₄-based MRI contrast agent and tumor-specific molecular probes, we studied the NaGdF₄ nanoparticle-based MRI probes. Differently sized NaGdF₄ nanocrystals with narrow particle size distributions were synthesized by a high temperature approach. Upon ligand exchange, the as-prepared hydrophobic NaGdF₄ nanocrystals were transferred into water by using asymmetric PEGs simultaneously bearing phosphate and maleimide groups. Further investigations demonstrated that the water-soluble NaGdF₄ nanocrystals, coated by PEG bearing two phosphate groups on the same side, exhibit not only excellent colloidal stability in water and PBS buffer, but also higher T1 relaxivity than Gd-DTPA (Magnevist^®). Through “click” reaction between the maleimide residue on particle surface and thiol group from the partly reduced anti-EGFR monoclonal antibody (mAb), NaGdF₄-PEG-mAb nanoprobes were constructed and their biocompatibility and binding specificity were evaluated through in vitro experiments. A series of in vivo experiments were then carried out for detecting intraperitoneal tumor xenografts in nude mice by using magnetic resonance (MR) imaging technique. The results have been accepted by ACS Nano recently.
    This work is a collaborated research by three groups with different research disciplines, including Prof. Mingyuan Gao’s group from Institute of Chemistry, CAS, Prof. Hao Lei’s group from Wuhan Institute of Physics & Mathematics, CAS, and Prof. Fan Wang’s group from Medical Isotopes Research Center, Peking University. Prof. Gao’s kindly supervise and discussion with other groups make the research work smoothly. What impressed me most is Prof. Gao’s patient instruction and help. Thanks to his patient guidance, my scientific quality has been trained, and also my abilities on communication and cooperation have been greatly improved.
                                                                                                                                                                                                          Yi Hou et al.