Synthesis Of Ultra-small Magnetic Nanoparticles And Their Applications In Magnetic Resonance Imaging

In vivo imaging is of great significance for basic research and diagnosis and treatment of clinical diseases,and the performance of the probe and the ability to reach and stay in the target tissue through the circulatory system are critical to the imaging effect.This subject mainly studies the synthesis of ultra-small-sized iron oxide nanoparticles and their magnetic resonance imaging performance.Iron oxide nanomaterials,which have always been used as T₂contrast agents,are shown to be T₁-T₂double by adjusting their size and doping metals.The effectiveness of modal imaging lays the foundation for rapid,sensitive and accurate early diagnosis and treatment of major diseases.（1）Using high temperature thermal decomposition method,using iron acetylacetonate as a precursor,adjusting the amount of stabilizer,reducing agent,and controlling the reaction temperature,to synthesize a series of ultra-small diameter iron oxide nanoparticles.The crystal form,morphology,magnetic properties and magnetic resonance imaging effects were studied,and the optimization rules of high-sensitivity magnetic resonance imaging nanoprobes were explored.By studying the influence of various factors,it is concluded that the lateral relaxation efficiency of 2.3 nm iron oxide nanoparticles r₁is 5.96 m M^-1s^-1,r₂/r₁is 4.06,which is more excellent than the clinically used gadolinium complex contrast agent(r₁=4 m M^-1s^-1),animal in vivo imaging results show that it has excellent T₁-T₂dual-mode contrast effect,and further vascular imaging studies found that the material also has a significant angiography effect.Therefore,this ultra-small size iron oxide nanoparticles are expected to be used as a multifunctional bimodal contrast agent for medical imaging diagnosis.（2）Element doping is an effective means to adjust various properties of nanomaterials.In this study,by doped Gd³⁺or Mn²⁺into ultra-small-sized iron oxide nanoparticles,the magnetic resonance imaging performance can be effectively improved.The results show that with the increase of gadolinium ion incorporation,the r₁value gradually increases and the longitudinal relaxation efficiency r₁can reach 6.05 m M^-1s^-1.Compared with undoped iron oxide nanoparticles,it is greatly improved.In vivo imaging shows a more intense bright contrast image,and highlights the details of blood vessels in the image.The iron oxide nanoparticles doped with manganese ions have a significant increase in saturation magnetization.Although the longitudinal relaxation rate is not as good as that of gadolinium doped nanoparticles,they still show a more obvious T₁-T₂dual mode in in vivo imaging.Imaging effect.（3）Co-doping the iron oxide nanoparticles with Gd³⁺ions and Mn²⁺to obtain double-doped iron oxide nanoparticles with uniform particle size and regular morphology.The particle size distribution is 3.3-5.4 nm.The magnetic interactions between the three metal atoms in the mixed magnetic iron oxide nanoparticles are for further study.The colloidal stability and blood compatibility of double-doped nanoparticles were evaluated.The results showed that the nanoparticles had good biocompatibility.To further verify the in vivo imaging effect,the above results show the most obvious positive and negative contrast images in this study,and the circulation time in vivo exceeds 60 min.It proves that the gadolinium-manganese bimetallic co-doping has achieved excellent T₁-T₂dual-mode imaging effect,which broadens the research ideas for the future study of ultra-small-size iron oxide particle contrast agents.