Paramagnetic dysprosium oxide nanoparticles and dysprosium hydroxide nanorods as T ₂ MRI contrast agents

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 ( ⁶H _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=3.2nm) and dysprosium hydroxide nanorods (20×300nm) are investigated. These include hydrodynamic diameters, magnetic properties, MR relaxivities, cytotoxicities, and 3tesla invivo T ₂ MR images. Here, MR imaging properties of dysprosium hydroxide nanorods have not been reported so far. These two samples show r ₂s of 65.04 and 181.57s ^-1mM ^-1, respectively, with negligible r ₁s at 1.5tesla and at room temperature, no invitro cytotoxicity up to 100μM Dy, and clear negative contrast enhancements in 3tesla invivo 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 3tesla.