abstract
The NMR relaxivities of the decatungstolanthanoate core-shell nanoparticles, prepared by encapsulating [Ln(W5O18)(2)](9-) polyoxometalates (LnPOM) within amorphous silica shells (K-9[Ln(W5O18)(2)]@SiO2), were studied along the Ln series. The relaxivity of GdPOM is slightly higher than for Gd-DTPA due to second-sphere relaxation effects, but the values for the other paramagnetic LnPOMs are much smaller due to the short T-1e values of their Ln(3+)-ions. The NPs have core-shell spherical structures, with LnPOM-containing cores with 9.5-28 nm diameters, and 4.0-11.0 nm thick amorphous silica shells. In water suspensions, the NPs have negative zeta potentials (-32.5 to -40.0 mV) and time-dependent hydrodynamic diameters (31-195 nm) reflecting the formation of aggregates. The relaxivities of GdPOM@SiO2 NPs suspensions (r(1)=10.97 (mM Gd)(-1) s(-1), r(2)=12.02 (mM Gd)(-1) s(-1), 0.47 T, 25 degrees C) are considerably larger than for the GdPOM solutions, indicating that their silica shell is significantly porous to water. This increase is limited by the agglomeration of the complexes in the NPs core, limiting their access to water to those at the core surface. Replacing half of the Gd3+ ions by Eu3+ decreases the NPs r(1) and r(2) relaxivities at 0.47 T to 20 % and 35 % of their initial values, which are still considerable, but does not affect the efficient luminescence properties of the Eu3+ centers. This indicates that the mixed NPs have potential as dual modality MRI/optical imaging contrast agents.
keywords
NMR TRANSVERSAL RELAXIVITY; MAGNETIC-RESONANCE; GOLD NANOPARTICLES; HETEROPOLYTUNGSTATE COMPLEXES; GADOLINIUM COMPLEX; GD(III) COMPLEXES; SI-29 NMR; PARTICLES; COORDINATION; SUSPENSIONS
subject category
Chemistry, Inorganic & Nuclear
authors
Carvalho, RFS; Pereira, GAL; Rocha, J; Castro, MMCA; Granadeiro, CM; Nogueira, HIS; Peters, JA; Geraldes, CFGC
our authors
Carlos Miguel Cardeal Enes Granadeiro
Post-Doc Fellowship
Helena Isabel Seguro Nogueira
Assistant Professor with Aggregation
João Rocha
Full Professoracknowledgements
This work was developed within the scope of the project CICECOAveiro Institute of Materials, UIDB/50011/2020 & UIDP/50011/2020, financed by national funds through the Portuguese Foundation for Science and Technology (FCT)/MCTES. CFGCG thanks the FCT for funding the Coimbra Chemistry Centre through the programmes UIDB/00313/2020 and UIDP/00313/2020, also cofunded by FEDER/COMPETE 2020-EU.