Monodispersed ferrite nanospheres were synthesized in an ethylene glycol/diethylene glycol (EG/DEG) binary solvent by using poly(vinylpyrrolidone) (PVP) as the surfactant. Particle size control can be attained by careful adjustment of the V_EG /V_DEG ratio. Different from previous reports, the magnetic studies of our iron ferrite (Fe₃O₄) nanospheres with various sizes from 20 to 300 nm reveal that they exhibit a similar magnetic saturation (M_s) value. In particular, both the ferromagnetic and superparamagnetic Fe₃O₄ nanospheres with similar M_s can be selectively obtained by varying the H₂O concentration in the reaction system. The magnetic resonance imaging (MRI) characterization indicates that the as-prepared superparamagnetic Fe₃O₄ and ZnFe₂O₄ nanospheres possess a T₂ relaxivity range that can be used as potential MRI contrast agents.

A facile synthesis of monodispersed microparticles composed of superparamagnetic Fe₃O₄ cores, SiO₂ shell, hierarchical γ-AlOOH periphery with Au nanoparticles is reported. These particles are found to be useful for protein immobilization and bear resemblance to daisy flowers, and are hereafter termed “nanoflowers”.