Robust dithiocarbamate-anchored amine functionalization of Au nanoparticles

We introduce an effective and facile technique that achieves robust amine functionalization of Au nanoparticles by binding the polyamine poly(allylamine hydrochloride) (PAH) to the surface using a dithiocarbamate (DTC) modification of the side group amines. The DTC anchor confers superior short- and long-term colloidal stability compared to a physisorbed layer of the same polymer. We also demonstrate that the surface amines are available for further functionalization and that at least four alternately charged polyelectrolyte layers can be assembled onto the particles. The latter modification could not be performed on a physisorbed functional layer, so this demonstrates the effectiveness of the DTC groups in robustly anchoring the polymer to the particle surface. At the same time, the DTC-anchored polymer layer is less than 2 nm thick in the dry state. This is one-third of the thickness of a physisorbed polyamine layer deposited under the same conditions, and sufficiently thin that the plasmonic field enhancement on the metal particle remains accessible to the outside environment. We attribute the difference in thickness to multiple DTC bonds on each polymer chain forcing it into much closer conformity to the particle surface than in the physisorbed case.