Selective anchoring of Gd(III) chelates on the external surface of organo-modified mesoporous silica nanoparticles: a new chemical strategy to enhance relaxivity.

The optimization of the physico-chemical properties of both Gd(III) chelates and nanocarriers is of great importance for the development of effective nanosystems for magnetic resonance imaging (MRI) applications. With this aim, macrocyclic Gd(III) chelates were selectively attached to the pendant amino groups exposed to the external surface of spheroidal mesoporous silica nanoparticles (MSNs). This was achieved by treating the metal complexes with MSNs that contained the templating surfactant molecules confined within the silica channels (hexadecyltrimethylammonium (CTA)/MSN), followed by extraction of the surfactant. The nanoparticles showed greatly improved (1)H relaxometric efficiency relative to corresponding systems that also feature Gd(III) chelates conjugated inside the pores. A further significant relaxivity enhancement was observed after chemical transformation of the free amino groups into amides. The ionic relaxivity of the final nanoparticles (r(1p) =79.1 mM(-1) s(-1); 0.5 T, 310 K) is one of the highest reported so far.