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Abstract

Spherical, nonporous and monodisperse silica nanoparticles (NPs) with a diameter of about 100 nm were synthesized and covalently functionalized with lanthanoid(III) (Ln = Gd or Y) chelate complexes, which serve as contrast agents (CAs) for magnetic resonance imaging (MRI). The materials were fully characterized after each synthetic step by different analytical methods, such as dynamic light scattering, scanning electron microscopy, DRIFT and NMR spectroscopy, thermogravimetry and elemental analysis, as well as zetapotential measurements. High surface concentrations of Gd(III) complexes (up to 50 μmol g−1) were determined by ICP-AES and T1-measurements, respectively. MRI experiments show the typical concentration-dependent increase of the longitudinal relaxation rate. T1-weighted images of samples with more than 25 μg NPs per 100 μL agar display a clear contrast enhancement in the agar layer. The transverse relaxivities r2 of the materials are significantly higher than r2 of the corresponding free Gd(III) complexes in water and medium, whereas the longitudinal relaxivities r1 are slightly increased. Due to the high loading of Gd(III) complexes, the relaxivities per particle are remarkably high (up to 2.78 × 105 mM−1 s−1 for r1). Thus, new hybrid materials, based on nonporous silica NPs with high local relaxivity values were synthesized, which can serve as very effective CAs for MRI.