Synthesis of Gd-dendrimers and transmission electron microscopy of higher generation Gd-dendrimers. A) A two-dimensional representation of naked polyamidoamine dendrimers up until generation 3 showing ethylenediamine core. B) The naked dendrimer has a cationic exterior. Functionalizing the terminal amine groups with Gd-diethyltriaminepentaacetic acid (charge -2) neutralizes the positive charge on the dendrimer exterior. C) Annular dark-field scanning transmission electron microscopy images of Gd-G5, Gd-G6, Gd-G7, and Gd-G8 dendrimers adsorbed onto an ultrathin carbon support film. Scale bar = 20 nm.