(2.17 ± 0.11 nm -2 ). This less dense packing is exploited by a second self-assembly step with the alkyl molecules in order to form binary SAMs on the nanoparticle surface. These systems, PAC3Imi+/PAC16@SPIONs and PAC3Imi+/PAC10Ph@SPIONs, combine the orthogonal properties of the individually modified SPIONs (increasing vs. decreasing ζ-potential, less vs. more dense) on one surface (see Figures , supplementary information).