Manganese-Loaded Dual-Mesoporous Silica Spheres for Efficient T1- and T2-Weighted Dual Mode Magnetic Resonance Imaging

A novel class of manganese-based dual-mode contrast agents (DMCAs) based on the core-shell structured manganese-loaded dual-mesoporous silica spheres (Mn-DMSSs) for simultaneous T1- and T2-weighted magnetic resonance imaging (MRI) has been successfully reported. The in vitro MR tests demonstrate that the Mn-based DMCAs display an excellent simultaneous T1-weighted and T2-weighted MR imaging effect with a noticeably high T1 relaxivity (r(1)) of 10.1 mM(-1)s(-1) and a moderately high T2 relaxivity (r(2)) of 169.7 mM(-1)s-(1). The Mn-based DMCAs exhibit negligible cytotoxicity with >80% cell viability at a concentration of up to 200 mu g/mL in human liver carcinoma (HepG2) and mouse macrophage (RAW264.7) cells after 24 Confocal laser scanning microscopy (CLSM) results show that the Mn-DMSSs were internalized via endocytosis and located in the cytoplasm but not in the nucleus. The in vivo experiment shows that the signals of rat liver increased by 29% under T1-weighted imaging mode and decreased by 28% under T2-weighted imaging mode in 5 mm postinjection of Mn-DMSSs, which reveal that the novel Mn-loaded DMSSs can be used as both positive (T1-weighted) and negative (T2-weighted) MR contrast agents in further biomedical applications.