Figure 1

Synthesis of gadolinium (Gd)-diethyltriaminepentaacetic acid (DTPA) conjugated polyamidoamine (PAMAM) dendrimers and images of higher generation (G) Gd-dendrimers with annular dark-field scanning transmission electron microscopy. A) Illustrations of naked PAMAM dendrimer generations from the ethylenediamine core (G0) to generation 3 (G3). The exterior of naked PAMAM dendrimers is positively charged due to the presence of terminal amine groups. The number of terminal amine groups doubles with each successive generation. B) Synthetic scheme for the production of Gd-DTPA conjugated PAMAM dendrimers. The conjugation of Gd-DTPA (charge -2) to the terminal amine groups 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. The average diameter of sixty Gd-G7 dendrimers is 11.0 ± 0.7 nm and that of sixty Gd-G8 dendrimers is 13.3 ± 1.4 nm (mean ± standard deviation). Scale bar = 20 nm. Adapted from reference[73].