Validation of Inner, Second, and Outer Sphere Contributions to T1 and T2 Relaxation in Gd3+-Based Nanoparticles Using Eu3+ Lifetime Decay as a Probe
Date
2018-05
Authors
Dash, Armita
Blasiak, Barbara
Tomanek, Boguslaw
van Veggel, Frank C.J.M.
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Journal ISSN
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Publisher
The Journal of Physical Chemistry C
Abstract
Paramagnetic lanthanide-based NPs are currently designed as magnetic resonance imaging (MRI) contrast agents to obtain optimal relaxivities at high magnetic fields of 7, 9.4 and 11.7 T where human imaging has been possible yielding high contrast to noise ratio in the MR images compared to the clinical field of 3 T. However, the underlying longitudinal (T1) and transverse (T2) relaxation mechanisms of the NP-based contrast agents based on the spatial motion and proximity of water protons with respect to the paramagnetic ions on the surface of NPs are still not well understood, specifically, in terms of contributions from inner, second, and outer spheres of coordination of water molecules to the NPs. Gd3+-based NPs, e.g., NaGdF4, are promising T1 contrast agents owing to the paramagnetic Gd3+ possessing a symmetric 8S7/2-state and slow electronic relaxation relevant to its efficiency to produce a positive (T1) contrast. Here, water-dispersed NaGdF4:Eu3+ (3 nm diameter, TEM) and NaYF4-NaGdF4:Eu3+ core-shell NPs (18.3 nm core diameter with 0.5 nm thick shell, TEM) were studied for their r1 and r2 relaxivities at 9.4 T. Excited state lifetime decays of Eu3+ dopants, which are highly sensitive to proximate water molecules, were analyzed, demonstrating a dominance of inner and second sphere contribution over outer sphere to the T1 and T2 relaxations in smaller NaGdF4:Eu3+ NPs while exclusively outer sphere in NaYF4-NaGdF4:Eu3+ core-shell NPs.
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Citation
Dash, A., Blasiak, B., Tomanek & van Veggel, F.C.J.M. (2018). Validation of Inner, Second, and Outer Sphere Contributions to T1 and T2 Relaxation in Gd3+-Based Nanoparticles Using Eu3+ Lifetime Decay as a Probe. The Journal of Physical Chemistry C, 122(21), 11557-11569. http://dx.doi.org/10.1021/acs.jpcc.8b02807