Facile synthesis and characterization of PTA stabilized hydrophilic Au55 nanoparticles via a DEN-MPC method

A dendrimer micelle:Au ratio of 1:55 is used to form Au55 dendrimer encapsulated nanoparticles (DENs). These seed crystals however undergo rapid twinning to form nanoparticles of increased cluster sizes. This is due to the nanoparticles not being fully stabilized by the dendrimer. These nanoparticles are then extracted from the dendrimer micelle template using PTA as a stabilizer in aqueous media. The large nanoparticles undergo a “divide and protect” mechanism upon prolonged exposure to the stabilizer. This leads to smaller nanoparticles which are stabilized by the PTA ligand to form monolayer protected clusters (MPC's). After an extraction time of 24 h, monodisperse nanoparticles with a diameter of 1.5 nm are obtained, which corresponds to the size of Au55 clusters.57