Paramagnetic dysprosium oxide nanoparticles and dysprosium hydroxide nanorods as T₂ 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 ((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.