The r relaxivity and T imaging properties of dendrimer-based manganese and gadolinium chelators in magnetic resonance imaging.

We report the preparation and characterization of gadolinium (Gd)- or manganese (Mn)-loaded dendrimers and Gd-loaded dendrimer-entrapped gold nanoparticles (Gd-Au DENPs) to examine the relationship between the number of metal ion chelators and r relaxivity. In this study, amine-terminated fifth-generation poly(amidoamine) dendrimers (G5.NH) modified with different numbers of DOTA-NHS chelators were used to chelate Gd and Mn ions. The remaining amine groups were then acetylated completely, followed by the use of materials with better r relaxivities and T-weighted imaging performances as templates to synthesize Gd-Au DENPs. The Gd and Mn chelators as well as Gd-Au DENPs were characterized different techniques. We show that the r relaxivity and T imaging performance increase with loading of greater numbers of Gd and Mn ions on the G5.NH and that the acetylation process affects the relaxivity and imaging properties to a certain extent. After entrapment with Au NPs, the r relaxivity and T-weighted imaging performance of Gd-Au DENPs decrease with greater loading of Au NPs. This systematic study of the relaxivities and T-weighted imaging performances of Gd, Mn, and Gd-Au DENP chelators are expected to be a theoretical basis for developing multifunctional dual-mode contrast agents.