Paramagnetic complexes containing
gadolinium ions have been widely used for magnetic resonance imaging (MRI) in clinic. However, these paramagnetic complexes pose some safety concerns. There is still a demand for the development of stable MRI
contrast agents that exhibit higher sensitivity and superior functionality to existing
contrast agents. Here, we develop carbonized paramagnetic complexes of
manganese (II) (Mn@CCs) to encapsulate Mn2+ in sealed carbonized shells with superhigh r1 relaxivity. Compared to the most common clinical
contrast agent Magnevist, investigations in vivo demonstrate that the Mn@CCs cross the intact blood-brain barrier of normal health mice with minor
metal deposition; preferentially target the
glioma tissues distribute homogeneously with high penetration in an intracranial mouse model; delineate clear
tumor margins in MRIs of ultrasmall single-nodule
brain tumors, and multi-nodular liver
tumors. The sensitivity, accuracy and low toxicity offer by Mn@CCs provides new opportunities for early molecular diagnostics and imaging-guided biomedical applications.