Programmed assembly of binary nanostructures in solution

Near size-monodisperse silver nanocrystals and silica nanospheres have been prepared and surface-modified with the [2]pseudorotaxane recognition motifs, dibenzo[24]crown-8 and dibenzylammonium cation, respectively. The silver nanocrystals, 7 nm in diameter, are shown to recognize and bind to the silica nanospheres, 180 nm in diameter, via pseudorotaxane formation. The result is the templated assembly of silver nanocrystals at the surface of the larger silica nanosphere core. This composite material exhibits optical properties that are a consequence of localizing silver nanocrystals at the surface of the silica nanospheres. The templating process is also shown to be reversible. This noncovalent recognition-directed templating strategy represents a novel metallization process resulting in the formation of composite media whose collective properties can be controlled.