Accurate bioimaging of internal body tissues plays a key role in achieving precise medical diagnosis. Magnetic resonance imaging (MRI) as one of the clinically used bioimaging modalities is largely hampered by the occurrence of false-positive imaging (artifacts). The use of contrast agents has tremendously contributed to the improvement of the accuracy of MRI, however, developing a dual-responsive contrast agent that capable of effectively switching from T₂ to T₁ contrast enhancement in vivo still remains a challenge. Here, we demonstrated the synthesis of a glutathione (GSH) and H₂O₂ dual-responsive “signal inversion” contrast agent, which mainly comprised of superparamagnetic iron oxide nanoparticles (SPION) and degradable mesoporous silica nanoparticles (DMSN). The contrast agent achieved T₂-weighted imaging in tumor site, and enabled an efficacious switch to T₁-weighted imaging upon the GSH- and H₂O₂-mediated degradation of DMSN. The characteristics of the signal transformation largely reduced the artifacts to enhance the accuracy of MRI. Interestingly, the in vivo evaluations revealed prominence of the T₂-weighted imaging up to 2 h post-intravenous injection, which was succeeded by T₁-weighted imaging that gradually increased with time and became dominant after 24 h. It was therefore expected that the findings shown in this work would guide the development of other contrast agents alike for more robust and accurate bioimaging by using MRI.

体内组织的准确生物成像在实现精确的医学诊断中起着关键作用。磁共振成像 (MRI) 作为临床使用的生物成像方式之一在很大程度上受到假阳性成像（伪影）的影响。造影剂的使用极大地促进了 MRI 准确性的提高，然而，开发一种能够在体内有效地从T ₂到T ₁对比度增强的双响应造影剂仍然是一个挑战。在这里，我们展示了谷胱甘肽 (GSH) 和 H ₂ O ₂的合成双响应“信号反转”造影剂，主要由超顺磁性氧化铁纳米颗粒（SPION）和可降解介孔二氧化硅纳米颗粒（DMSN）组成。造影剂在肿瘤部位实现了T ₂加权成像，并能够在 GSH和 H ₂ O ₂介导的 DMSN 降解后有效切换到T ₁加权成像。信号变换的特点大大减少了伪影，提高了MRI的准确性。有趣的是，体内评估揭示了静脉注射后长达 2 小时的T ₂加权成像的显着性，T ₁成功了- 加权成像随时间逐渐增加并在 24 小时后成为主导。因此，预计这项工作中显示的发现将指导其他造影剂的开发，以便通过使用 MRI 实现更强大和准确的生物成像。