Divalent metal ion-mediated assembly of spherical nucleic acids: the case study of Cu2+

Despite the critical functions of divalent metal ions (M2+ s) in association with duplex DNA, fundamental and general interactions of M2+ s with spherical nucleic acids (SNAs) composed of single-stranded DNA have rarely been investigated. We have explored that the coordinative nature of the M2+-SNA binding mediates the temperature-and base composition-dependent reversible assemblies of SNAs even without the need of complementary counterparts for duplex-interconnection, additional monovalent metal ions for charge screening, or pre-designed sequences for any non-Watson-Crick base-pairing, all of which are essential for the conventional assembly of SNAs. Cu2+ has been identified to maximize the reversible assembly properties in relation to this M2+-mediated DNA bond, and has been further qualitatively and quantitatively investigated in detail as a model system.