The r(1) relaxivity and T(1) 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(1) relaxivity. In this study, amine-terminated fifth-generation poly(amidoamine) dendrimers (G5.NH(2)) 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(1) relaxivities and T(1)-weighted imaging performances as templates to synthesize Gd-Au DENPs. The Gd and Mn chelators as well as Gd-Au DENPs were characterized via different techniques. We show that the r(1) relaxivity and T(1) imaging performance increase with loading of greater numbers of Gd and Mn ions on the G5.NH(2) and that the acetylation process affects the relaxivity and imaging properties to a certain extent. After entrapment with Au NPs, the r(1) relaxivity and T(1)-weighted imaging performance of Gd-Au DENPs decrease with greater loading of Au NPs. This systematic study of the relaxivities and T(1)-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.