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A series of zeolite-type silicates containing stoichiometric amounts of Ln3+ ions in the framework (Ln-AV-9 materials), with composition (Na4K2)(Ln2Si16O38)·10H2O (Ln = Nd, Sm, Eu, Tb, Gd, Dy) has recently been synthesized and characterized. They form paramagnetic microparticles, which as aqueous suspensions have negligible water 1H longitudinal relaxivities (r1) for all Ln3+ ions studied and quite large transverse relaxivities (r2). In this work we further analysed the size distribution of the Ln-AV-9 particles and their r2* and r2 relaxivities. The r2* relaxivity effects are explained by the static dephasing regime (SDR) theory. The r2 relaxivities appear to be strongly dependent on the interval between two consecutive refocusing pulses (τCP) in the train of 180° pulses applied. For long τCP values, the r2 of the systems saturates at a value, which is always an order of magnitude smaller than r2*. These features are explained by a crude model, which takes into account the residual diffusion effect in the static dephasing regime. The large microparticles, although not efficient in T1 relaxation, are quite effective in enhancing T2 relaxation, particularly at high magnetic fields. The r2* values and the saturation values for r2 were found to increase linearly with B0 and μ02. The largest transversal relaxation rate enhancements were observed for Dy-AV-9 with a saturation value of r2 of 60 s−1 mM−1 and a r2* value of 566 s−1 mM−1 at 9.4 T and 298 K. [ABSTRACT FROM AUTHOR]

The first examples of nanoparticles of pure layered Ln 2(SiO 4H)(OH) 2(H 2O)Cl (where Ln = Eu, Gd, and Tb) and mixed microcrystalline layered lanthanide silicates containing different Eu/Gd and Tb/Gd ratios have been reported. The crystal structure of these silicates has been solved from synchrotron powder X-ray diffraction data. These materials display interesting and tuneable photoluminescence (PL) properties, such as energy transfer between different Ln 3+centers, illustrated here with the pairs Eu 3+/Gd 3+and Tb 3+/Gd 3+. The PL properties of the mixed Eu 3+/Gd 3+sample change upon F –for Cl −ion exchange, and this raises the possibility that this material may be exploited for sensing these ions. [ABSTRACT FROM AUTHOR]

This work reports on highly fluorescent and superparamagnetic bimodal nanoparticles (BNPs) obtained by a simple and efficient method as probes for fluorescence analysis and/or contrast agents for MRI. These promising BNPs with small dimensions (ca. 17 nm) consist of superparamagnetic iron oxide nanoparticles (SPIONs) covalently bound with CdTe quantum dots (ca. 3 nm). The chemical structure of the magnetic part of BNPs is predominantly magnetite, with minor goethite and maghemite contributions, as shown by Mössbauer spectroscopy, which is compatible with the x-ray diffraction data. Their size evaluation by different techniques showed that the SPION derivatization process, in order to produce the BNPs, does not lead to a large size increase. The BNPs saturation magnetization, when corrected for the organic content of the sample, is ca. 68 emu g−1, which is only slightly reduced relative to the bare nanoparticles. This indicates that the SPION surface functionalization does not change considerably the magnetic properties. The BNP aqueous suspensions presented stability, high fluorescence, high relaxivity ratio (r2/r1 equal to 25) and labeled efficiently HeLa cells as can be seen by fluorescence analysis. These BNP properties point to their applications as fluorescent probes as well as negative T2-weighted MRI contrast agents. Moreover, their potential magnetic response could also be used for fast bioseparation applications. [ABSTRACT FROM AUTHOR]