Synthesis And Characterization Of Laponite-stabilized Iron Oxide Nanoparticles For Nucler Magnetic Resonance Imaging Applications

Magnetic iorn oxide nanoparticles（Fe₃O₄ NPs） have been extensively explored for biomedical application, especially in the field of magnetic resonance imaging（MRI） due to their intristic superparamagnetism, high saturation magnetization and low toxicity. However, Fe₃O₄ NPs tend to aggregate without surface modification and their T2 relaxivity always declines after surface modification, therefore, these drawbacks hinder Fe₃O₄ NPs to be used as an effective T2 contrast agent. In this case, it is highly needed to select desirable carriers to mediate the synthesise of Fe₃O₄ nanoplatform with improved T2 relaxivity, good colloidal stability, followed by modification of targeting ligand which can improve the targeting imaging effect of tumors. In addition, it is expected to realize theranostic of cancer through further loading anti-cancer drugs.In this research, laponite（LAP） with good colloidal stability was selected as the stabilizer to synthesize multifunctional LAP-stablized Fe₃O₄（LAP/Fe₃O₄） nanoplatform. First, the stable LAP/Fe₃O₄ NPs were synthesized by a facile controlled coprecipitation method in the presence of LAP. Then, the properties of the formed LAP/Fe₃O₄ NPs, such as morphology, size distribution, zeta potential, hydrodynamic size, and r2 relaxivity were extensively characterized by various techniques, and the results show that LAP/Fe₃O₄ NPs own several important advantages including water-dispersibility and improved T2 relaxitivity when compared to naked Fe₃O₄ NPs（475.9 mM-1s-1 vs 247.61 mM-1s-1）. The result of cell viability assay reveals that LAP/Fe₃O₄ NPs possess excellent cytocompatibility. Both in vitro cellular MR imaging and in vivo MR imaging of tumor showed obvious signal change after treatment of LAP/Fe₃O₄ NPs owing to the specific cellular uptake of those NPs. In addition, an obvious signal change also can be seen in the liver and kidney. The results of bioditribution and histological examination show that the LAP/Fe₃O₄ NPs can be gradually metabolized from living body without side effectsIn order to realize specific accumulation of LAP/Fe₃O₄ NPs in tumor site and prevent unspecific uptake of NPs by normal tissue, in this work, we modified LAP/Fe₃O₄ NPs with amphiphilic block copolymer polylactic acid-polyethylene glycol（PLA-PEG-COOH） by hydrophobic interaction, and then convalently conjugated with G2-FA via EDC coupling chemistry. Our results show that the synthesized LAP/Fe₃O₄-PLA-PEG-G2-FA NPs have a high r2 relaxivity and good cytocompatibility within a given concentration. The experimental results about in vitro cellular MR imaging and in vivo MR imaging of tumors demonstrate the good targeting ability of the NPs to cancer cells overexperssing FA receptor, resulting in specific uptake by cancer cells and accumulation in tumor tissue as well as realizing targeted MR imaging of cancer cells in vitro and tumor in vivo. Therefore, LAP/Fe₃O₄-PLA-PEG-G2-FA NPs hold great promise to be used as MR imaging contrast agent for the early diagnosis of cancer.