Targeted T₁–T₂ MRI contrast agents, which can eliminate the difficulty of image matching across multiple imaging instruments and permit specific localization of lesions, are promising candidates for more accurate diagnosis of tumors. In this study, ultrasmall Fe@Fe₃O₄ nanoparticles were designed and synthesized as T₁–T₂ dual-mode MRI contrast agents for accurate tumor imaging. First, to investigate the influence of nanoparticle size, Fe@Fe₃O₄ nanoparticles with diameters of 4, 8, and 12 nm were prepared, among which the 8 nm 3-(3,4-dihydroxyphenyl)propionic acid (DHCA)-modified nanoparticles exhibited the optimal T₁–T₂ dual-mode MRI performance. Next, to develop a tumor-targeted contrast agent, the DHCA-Fe@Fe₃O₄ nanoparticles were conjugated with the F56 peptide, which targets the vascular endothelial growth factor receptor, and the resulting F56-DHCA-Fe@Fe₃O₄ nanoparticles were found to exhibit good T₁–T₂ dual-mode imaging and tumor-targeting performance both in vitro and in vivo, indicating the nanoparticles represent a new research tool for accurate tumor diagnosis.

靶向T ₁ – T ₂ MRI 造影剂可以消除跨多个成像仪器进行图像匹配的困难并允许对病变进行特定定位，是更准确诊断肿瘤的有希望的候选者。在这项研究中，超小 Fe@Fe ₃ O ₄纳米粒子被设计和合成为T ₁ - T ₂双模式 MRI 造影剂，用于准确的肿瘤成像。首先，为了研究纳米颗粒尺寸的影响，Fe@Fe ₃ O ₄制备了直径为 4、8 和 12 nm 的纳米粒子，其中 8 nm 3-(3,4-二羟基苯基)丙酸 (DHCA) 修饰的纳米粒子表现出最佳的T ₁ - T ₂双模 MRI 性能。接下来，为了开发靶向肿瘤的造影剂，将 DHCA-Fe@Fe ₃ O ₄纳米颗粒与靶向血管内皮生长因子受体的 F56 肽结合，以及由此产生的 F56-DHCA-Fe@Fe ₃ O ₄发现纳米颗粒表现出良好的T ₁ – T ₂ 体外和体内的双模式成像和肿瘤靶向性能，表明纳米颗粒代表了准确肿瘤诊断的新研究工具。