Importantly, the two bands travelled the same distance as Au•TMA with Au•MUA, which had not been in contact with the oppositely charged NP. As a control experiment, we heated the Au•TMA/Au•MUA precipitate at 70 ºC, which induced ligand hopping between the NPs, affording a single NP type, i.e., Au⋅(TMA/MUA). The net charge of these NPs approached zero; hence, they did not migrate in an electric field. The methodology described here is general; we expect that when applied to mixtures of charged NPs of various sizes, shapes, and core compositions, it will lead to a wide range of new nanostructured materials.