Lanthanide vanadate-based nanoparticles as multimodal T1 -T2 MRI contrast agent and NIR luminescent imaging probe

We report the development of a multimodal lanthanide vanadate system suitable as dual T 1 -T 2 MRI contrast agent as well as a luminescent imaging probe in the near-infrared region, using Dy 3+ and Gd 3+ as T 2 and T 1 components, respectively, and Nd 3+ as the luminescent center. The vanadate matrix was chosen to avoid the undesired solubility associated to previously reported fluoride-based contrast agents . With such aim, we first optimized the design of the MRI system by comparatively evaluating the magnetic relaxivities of two different architectures consisting of i) uniform NPs incorporating both paramagnetic cations in solid solution (single-phase NPs), and ii) core-shell NPs consisting of a DyVO 4 core coated with a homogeneous GdVO 4 shell (DyVO 4 @GdVO 4 ). We found that, although both samples presented magnetic relaxivity properties that make them adequate for their use as dual T 1 -T 2 contrast agents for magnetic resonance imaging, the core-shell architecture would be more suitable because of their higher magnetic relaxivity values. Secondly, to prepare the multimodal system, the GdVO 4 layer of such optimal dual T 1 -T 2 MRI probe was doped with Nd 3+ cations. An inert YVO 4 intermediate shell was also introduced between the cores and the outer layer aiming to avoid energy transfer from Nd 3+ to Dy 3+ , which would cause luminescence quenching . These core-shell-shell nanoparticles showed magnetic relaxivity values similar to those of the core-shell system and an intense luminescence in the near-infrared region. Moreover, they were dispersible and chemically stable under conditions that mimic the physiological media, and they were nontoxic for cells. Therefore, such multimodal nanoparticles meet the main requirements for their use as a dual T 1 -T 2 contrast agent for magnetic resonance imaging and as a probe for luminescent imaging in the near-infrared region.