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).