Controlled synthesis of water-dispersible and superparamagnetic Fe₃O₄ nanomaterials by a microwave-assisted solvothermal method: From nanocrystals to nanoclusters

Highly tunable Fe₃O₄ nanocrystals and nanoclusters with excellent water-dispersible and superparamagnetic properties were successfully synthesized in 3 h by a facile, effective microwave-assisted solvothermal method in ethylene glycol (EG). The effects of the main reaction conditions, including the weight ratio of FeCl₃·6H₂O to NaAc·3H₂O, the reaction temperature and time, on the size and morphology of the resulting products were systematically examined, and highly tunable superparamagnetic Fe₃O₄ nanocrystals (12-25 nm) and nanoclusters (40-90 nm) were selectively prepared. In addition, the morphology, structure, magnetic properties, and T₂ magnetic resonance (MR) contrast capability of these Fe₃O₄ nanomaterials were investigated. The optimized superparamagnetic iron oxide nanoparticle (SPION) crystals and SPION clusters exhibited remarkable saturation magnetization values of 78.4 and 75.2 emu g^-1 and excellent r₂ relaxivities of 101.05 and 100.68 mM^-1 s^-1, respectively. Therefore, the resulting Fe₃O₄ nanomaterials demonstrate immense potential as MR imaging (MRI) contrast agents. This simple, efficient approach can also be used to synthesize other water-dispersible nanomaterials with a tunable size and morphology, good reproducibility, and high product yield.