Paramagnetic dysprosium oxide nanoparticles and dysprosium hydroxide nanorods as T2 MRI contrast agents

Abstract We report here paramagnetic dysprosium nanomaterial-based T 2 MRI contrast agents. A large r 2 and a negligible r 1 is an ideal condition for T 2 MR imaging. At this condition, protons are strongly and nearly exclusively induced for T 2 MR imaging. The dysprosium nanomaterials fairly satisfy this because they are found to possess a decent r 2 but a negligible r 1 arising from L  +  S state 4f - electrons in Dy(III) ion ( 6 H 15/2 ). Their r 2 will also further increase with increasing applied field because of unsaturated magnetization at room temperature. Therefore, MR imaging and various physical properties of the synthesized d -glucuronic acid coated ultrasmall dysprosium oxide nanoparticles ( d avg  = 3.2 nm) and dysprosium hydroxide nanorods (20 × 300 nm) are investigated. These include hydrodynamic diameters, magnetic properties, MR relaxivities, cytotoxicities, and 3 tesla in vivo T 2 MR images. Here, MR imaging properties of dysprosium hydroxide nanorods have not been reported so far. These two samples show r 2 s of 65.04 and 181.57 s −1 mM −1 , respectively, with negligible r 1 s at 1.5 tesla and at room temperature, no in vitro cytotoxicity up to 100 μM Dy, and clear negative contrast enhancements in 3 tesla in vivo T 2 MR images of a mouse liver, which will be even more improved at higher MR fields. Therefore, d -glucuronic acid coated ultrasmall dysprosium oxide nanoparticles with renal excretion can be a potential candidate as a sensitive T 2 MRI contrast agent at MR field greater than 3 tesla.