Using Gradient Magnetic Fields to Control the Size and Uniformity of Iron Oxide Nanoparticles for Magnetic Resonance Imaging

The size and uniformity of magnetic nanoparticles are essential for biomedical performance. In this study, we successfully controlled the size and uniformity of magnetic nanomaterials by applying gradient magnetic fields during the solvothermal method. This regulation method conforms to the following laws: the size of the synthesized magnetic nanoparticles (MNPs) is smaller when the applied magnetic field is stronger, and the synthesized uniformity is better when the product of the applied field and its gradient is greater. In vitro and in vivo magnetic resonance imaging experiments show that magnetic field treatment resulted in uniform MNPs of 4.5 nm, which can significantly improve the T₁ contrast performance. We further propose a dynamic process of field-induced reconfiguration for reverse micelles (re-micelles) to analyze how the gradient magnetic field affects MNP synthesis.