Synthesis, characterization, and surface immobilization of metal nanoparticles encapsulated within bifunctionalized dendrimers

Bifunctionalized poly(amidoamine) dendrimers having both quaternary ammonium groups and primary amines on their periphery were prepared. Pd and Pt nanoparticles were encapsulated within these dendrimers by extraction of the metal ions into their interior, followed by chemical reduction. The high positive charge on the surface of these dendrimers reduces the likelihood of agglomeration, and the unquaternized amine groups provide a reactive handle for immobilizing the dendrimer-encapsulated nanoparticles (DENs) onto surfaces. High-resolution transmission electron microscopy images reveal that both encapsulated Pd and Pt nanoparticles are nearly monodisperse with an average diameter of 1.7 +/- 0.3 nm. Pd and Pt DENs were immobilized onto An surfaces using an intermediary self-assembled monolayer as an adhesion layer. Only a small fraction of the resulting nanoparticle monolayer is lost when sonicated in an acidic aqueous solution or subjected to electrochemical cycling.