Core-Shell Structurized Fe3O4@C@MnO2 Nanoparticles as pH Responsive T1-T2* Dual-Modal Contrast Agents for Tumor Diagnosis.

Biocompatible core-shell Fe3O4@C@MnO2 nanoparticles (named as FOCMO NPs) with an average size at 130 nm prepared through an effortless yet efficient strategy were employed as pH-activatable T1-T2* dual-modality magnetic resonance imaging (MRI) contrast agents (CAs). The release rate of Mn ions in acidic PBS (pH = 5.0) was approximately 10 times to that under condition with pH value of 7.4. Benefiting from excellent acid responsiveness, which facilitates the release of ions from FOCMO NPs at tumor region with acidic microenvironment and organelles, the diagnosis accuracy was commendably improved. After intravenous injection of FOCMO NPs, an efficiently intensive contrast in tumors are realized with a distinct enhancement of 127% in T1 MRI signal 24 h after the administration. Moreover, a significant decreasement of 71% is witnessed in T2 MRI signal. Those demonstrated that FOCMO NPs can achieve the purpose of positive/negative MRI simultaneously. Furthermore, obtained FOCMO NPs showed great hemocompatibility and negligible toxicity.