The r1 relaxivity and T1 imaging properties of dendrimer-based manganese and gadolinium chelators in magnetic resonance imaging

Abstract

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 r1 relaxivity. In this study, amine-terminated fifth-generation poly(amidoamine) dendrimers (G5.NH2) 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 r1 relaxivities and T1-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 r1 relaxivity and T1 imaging performance increase with loading of greater numbers of Gd and Mn ions on the G5.NH2 and that the acetylation process affects the relaxivity and imaging properties to a certain extent. After entrapment with Au NPs, the r1 relaxivity and T1-weighted imaging performance of Gd-Au DENPs decrease with greater loading of Au NPs. This systematic study of the relaxivities and T1-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.