Preparation, Characterization, and Magnetic Resonance Imaging of Mn@SiO2 Nanowires

The deposition time was controlled to prepare Mn nanowires of different lengths and diameters on templates of anodic aluminum oxide (AAO) with different pore sizes. The surface of as-prepared Mn nanowires was modified with SiO₂ using the sol-gel method to improve their dispersion in aqueous solution. The effects of the diameter and length of the as-prepared Mn nanowires coated with SiO₂ on the relaxivity were investigated. It was found that the Mn@SiO₂ nanowires have smaller diameters and a higher longitudinal relaxivity (r₁) with an increased length. Mn3@SiO₂ nanowires had the highest r₁ value of 5.8 mM^-1 s^-1 among the Mn@SiO₂ nanowires (Mn3 nanowires have a diameter of about 30 nm and a length of about 0.5 μm length). Additionally, the biocompatibility and in vivo imaging ability of the Mn3@SiO₂ nanowires were evaluated. The Mn3@SiO₂ nanowires had good cytotoxicity and biocompatibility, and the kidney of SD rats showed a positive enhancement effect during small animal imaging at 1.5 T. This study showed that the Mn3@SiO₂ nanowires could potentially become contrast agents (CAs) of longitudinal relaxation time (T₁).