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Magnetic nanomaterials, especially superparamagnetic nanomaterials, are paid more attention on by people because of their special physical and chemical properties, and therefore they have a broad prospect of application in mechanical, electrical, optical, magnetism, chemical and biological field, especially in recent years, more people have been intrested in magnetic resonance imaging （MRI）. MRI technology frequently can realize "non-inasie", clear 3D imaging of the cells or human tissue, so it plays an important role in many fields. Magnetic nanoparticles are often used as the contrast agent in the field of MRI, and improve the contrast and clarity of MRI images. The development of magnetic nanoparticles brings new vitality and progress to the MRI technology.The experiments are divided into two parts, and we separately studied some applications of MnFe2O4 and Fe3O4 magnetic nanoparticles in MRI fields. The first part is the research of morphology and magnetic properties of MnFe2O4 magnetic nanoparticles. We used Fe（acac）3 and Mn（acac）2 as precursors; oleic acid, oleylamine and 1,2-hexadecane glycol and their mixture as surfactant. In organic solution, we synthesised the MnFe2O4 magnetic nanoparticles by high thermal decomposition. We studied the effect of various surfactants on the size of MnFe2O4 magnetic nanoparticles, shape and magnetic properties. Through the ligand exchange, exchange oil-soluble surfactants on iron acid manganese magnetic nanoparticles surface with hydrophilic molecules—dopamine, make nanoparticles is water-soluble, the materials were used for the further research on magnetic resonance imaging experiments of HeLa cells. The second part is Hg2+ MR sensing effect of Fe3O4 magnetic nanoparticles. First, we use Fe（acac）3 as precursors, oleylamine as surfactant, in organic solution, with high thermal decomposition to synthesis Fe3O4 magnetic nanoparticles. Then, the experiments were divided into two parts. The first method was ligand exchange, which made hydrophilic groups—amino on the surface of nanoparticles, then the material became soluble in aqueous solution. Through covalent modifition with Thymine, we synthesized Fe3O4@DA@T nanomaterials. The second method was to coat the shell of silica and modify amino on the surface of tne materials, and then we connected thymine through covalent bond, Fe3O4@SiO2@T nanomaterials were prepared at last. We conducted characterizations about size, shape, surface functional groups and magnetic and effect of Hg2+ selective—MR nanosensor in Hepes buffer solution of two nanoparticles through various methods. Experiments proved that two kinds of materials could be used as Hg2+ selective—MR nanosensor, but the materials synthesed by the second method was more selective and sensitivite as nanosensor than the other nanoparticles.In conclusion, we synthesized some iron chromate salt nanoparticles, separately studied them as MRI applications in Hela cells imaging and mercury ion sensing, and achieved the ideal effect.
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