Size-controlled synthesis of dendrimer-stabilized silver nanoparticles for X-ray computed tomography imaging applications

We report a facile size-controlled synthesis of dendrimer-stabilized silver nanoparticles (Ag DSNPs) for X-ray computed tomography (CT) imaging applications. Amine-terminated generation 5 poly(amidoamine) dendrimers were used as templates to complex Ag(I) ions for subsequent reductive formation of dendrimer-entrapped Ag nanoparticles. Following a one-step acetylation reaction to transform dendrimer terminal amine to acetyl groups, Ag DSNPs can be formed. The formed Ag DSNPs were characterized using H-1 NMR, UV-V is spectrometry, transmission electron microscopy, and zeta-potential measurements. We show that through the variation of the dendrimer/Ag salt molar ratio, the size of Ag DSNPs can be controlled at the range of 8.8-23.2 nm. The formed Ag DSNPs are stable not only in water, PBS buffer, and fetal bovine serum, but also at different pH conditions (pH 5-8) and temperatures (20-50 degrees C). X-Ray absorption coefficient measurements show that the attenuation of Ag DSNPs is size-dependent, and the Ag DSNPs with a diameter of 16.1 nm display an X-ray attenuation intensity close to that of a clinically used iodine-based contrast agent (Omnipaque) at the same molar concentration of the active element (Ag versus iodine). This suggests that Ag DSNPs with an appropriate size have a great potential to be used as a CT imaging contrast agent, although the atomic number of Ag is lower than that of iodine. Furthermore, CT scanning showed prolonged enhancement at the point of mice injected subcutaneously with Ag DSNPs, rendering them as a promising contrast agent in CT imaging applications.