Azido-Coated Nanoparticles: A Versatile Clickable Platform for the Preparation of Fluorescent Polystyrene Core-PAMAM Shell Nanoparticles

The convergent synthesis of fluorescent polystyrene core-PAMAM shell nanoparticles in the 15-20 nm diameter range is presented using azido-coated nanoparticles (NPN3) as a clickable platform. The coupling of the different partners occurs exclusively on the surface of the cross-linked polystyrene matrix owing to its nonswelling properties in water. PAMAM dendrons having an alkyne moiety at their focal point and peripheral carboxylic acid groups were covalently attached to the surface of azido-coated nanoparticles via a CuAAC reaction. Given the high density of azide anchoring groups on the NP surface (about 560 N-3 per NP) and the size of the PAMAM derivative, the grafting of dendrons was not complete, leaving azide units available for further functionalization with an alkyne dansyl derivative. These new dendron-coated nanoparticles, which possess a number of terminal functional groups comparable to the high eighth generation of PAMAM dendrimers, are obtained in a few steps without tedious chromatographic purification. Dendritic shell saturation levels of 70-85% were reached for these dendron-coated nanoparticles. The colloidal stability of the resulting scaffold was governed by the dendritic shell. Particularly, a pH-dependent electrostatic self-assembly process between the ammonium moieties of the cationic surfactant and carboxylate groups of PAMAM can be switched. This straightforward strategy gives access to dendron-coated nanoparticles as valuable building blocks for the construction of functional nanomaterials.