Mesoporous MnSiO₃@Fe₃O₄@C Nanoparticle as pH-responsive T₁-T₂^* Dual-modal Magnetic Resonance Imaging Contrast Agent for Tumor Diagnosis

Mesoporous structured MnSiO₃@Fe₃O₄@C nanoparticles (NPs) were prepared via a facile and efficient strategy, with negligible cytotoxicity and minor side efforts. The asprepared MnSiO₃@Fe₃O₄@C NPs hold great potential in serving as pH-responsive T₁-T₂^* dual-modal magnetic resonance (MR) imaging contrast agents. The released Mn²⁺ shortened T₁ relaxation time, meanwhile the superparamagnetic Fe₃O₄ enhanced T₂ contrast imaging. The release rate of Mn ions reaches 31.66% under the condition of pH=5.0, which is similar to tumor microenvironment and organelles. Cytotoxicity assays show that MnSiO₃@Fe₃O₄@C NPs have minor toxicity, even at high concentrations. After intravenous injection of MnSiO₃@Fe₃O₄@C NPs, a rapid contrast enhancement in tumors was achieved with a significant enhancement of 132% after 24 h of the administration. Moreover, a significant decreasement of 53.8% was witnessed in T₂ MR imaging signal. It demonstrated that MnSiO₃@Fe₃O₄@C NPs can act as both positive and negative MR imaging contrast agents. Besides, owing to the pH-responsive degradation of mesoporous MnSiO₃, MnSiO₃@Fe₃O₄@C NPs can also be used as potential drug systems for cancer theranostics.