Precisely Tuning the Contrast Properties of Zn_xFe_3–xO₄ Nanoparticles in Magnetic Resonance Imaging by Controlling Their Doping Content and Size

Given that the contrast of Zn-doped Fe3O4 nanoparticles (NPs) (ZnxFe3–xO4) in magnetic resonance imaging (MRI) depends on their intrinsic chemical and physical properties such as doping content or size, the ability to finely control these characteristics is very important but at the same time very challenging. In this work, we introduce a novel doping mechanism and present how various desired MRI contrast levels can be precisely achieved by synthesizing ZnxFe3–xO4 nanoparticles in a controlled and reproducible manner, exhibiting different Zn doping concentrations (ZnxFe3–xO4, x = 0/0.1/0.2/0.3/0.4) and different dimensions (4/7/10 nm). The experimental results show that ZnxFe3–xO4 NPs of a specific dimension form a system whose saturation magnetization and crystal structures can be easily tuned by adjusting their Zn doping contents. The proposed model thus enables the exact tuning of MRI contrast by controlling NP doping content and size. The utility of our study is not restricted to the case of the considered material, as it can be easily extrapolated and applied in the case of other divalent transition metal ion-doped magnetic NPs, to optimize their MRI contrast and eventually other relevant properties for further biomedical applications.