The exploration of magnetic resonance imaging (MRI) agents possessing excellent performances and high biosafety is of great importance for both fundamental science research and biomedical applications. In this study, we present that monodisperse Fe2O3 supraparticles (SPs) can act as T1-weighted MRI agents, which not only possess a distinct off-on MRI switch in the tumor microenvironment but also are readily excreted from living bodies due to its quasi-amorphous structure and hierarchical topology design. First, the Fe2O3 SPs have a surface-to-volume ratio obviously smaller than that of their building blocks by means of self-assembly processes, which, on the one hand, causes a rather low r1 relaxivity (0.19 mM-1 s-1) and, on the other hand, can effectively prevent their aggregation after intravenous injection. Second, the Fe2O3 SPs have a dramatic disassembly/degradation-induced active T1-weighted signal readout (more than 6 times the r1 value enhancement and about 20 times the r2/r1 ratio decrease) in the tumor microenvironment, resulting in a high signal-to-noise ratio for imaging performances. Therefore, they possess excellent in vivo imaging capacity, even with a tumor size as small as 5 mm3. Third, the disassembled/decomposed behaviors of the Fe2O3 SPs facilitate their timely clearance/excretion from living bodies. In particular, they exhibit distinct renal clearance behavior without any kidney damage with the right dosage. Fourth, the favorable biodegradability of the as-prepared Fe2O3 SPs can further relieve the concerns about the unclear biological effects, particularly on nanomaterials, in general.

中文翻译：

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准无定形和分级Fe2O3超粒子：体内和肾脏清除的主动T1加权磁共振成像。

具有优异性能和高生物安全性的磁共振成像（MRI）试剂的探索对于基础科学研究和生物医学应用都具有重要意义。在这项研究中，我们提出单分散的Fe2O3超颗粒（SPs）可以充当T1加权MRI剂，它们不仅在肿瘤微环境中具有独特的脱机MRI开关，而且由于其准分子也很容易从活体中排出。非晶结构和分层拓扑设计。首先，通过自组装过程，Fe2O3 SP的表面体积比明显小于其构造块，这一方面导致相对较低的r1弛豫度（0.19 mM-1 s-1 ），另一方面，可以有效地防止静脉注射后它们的聚集。第二，Fe2O3 SP在肿瘤微环境中具有显着的分解/降解诱导的主动T1加权信号读数（r1值增强的6倍以上，r2 / r1的比率下降的20倍以上），从而导致较高的信号与成像性能的噪声比。因此，即使肿瘤尺寸小至5 mm3，它们也具有出色的体内成像能力。第三，Fe2O3 SP的分解/分解行为有助于其及时从生物体内清除/排泄。特别地，它们以适当的剂量表现出明显的肾脏清除行为，而没有任何肾脏损害。第四，所制备的Fe2O3 SPs具有良好的生物降解性，这通常可以进一步缓解人们对生物效应不清楚的担忧，尤其是对纳米材料的生物效应。