Selfassembly of metallic nanoparticle arrays by DNA scaffolding

We report the self-assembly of metallic nanoparticle arrays using DNA crystals as a programmable molecular scaffolding. Gold nanoparticles, 1.4 nm in diameter, are assembled in two-dimensional arrays with interparticle spacings of 4 and 64 nm. The nanoparticles form precisely integrated components, which are covalently bonded to the DNA scaffolding. These results show that heterologous chemical systems can be assembled into precise, programmable geometrical arrangements by DNA scaffolding, thereby representing a critical step toward the realization of DNA nanotechnology. Several schemes in which DNA is used to assemble nanoparticles in specific geometrical arrangements have been reported, including (1) the formation of nanoparticle dimers and trimers by the attachment of nanoparticles to a single strand of DNA and subsequent hybridization to a target (Alivisatos et al., 1996), (2) the assembly of nanoparticles by using DNA as a selective adhesion material for ‘gluing’ objects together (Mirkin, 1996), and (3) the formation of supramolecular aggregates by self-assembly of DNA-streptavidin adducts (Niemeyer, 1998). The real potential of DNA nanotechnology will be realized, however, only when heterologous chemical systems have been scaffolded into precise, programmable geometrical arrangements. In this paper, we exploit the predictability of the local product structure in sticky-ended cohesion (Qiu et al., 1997) to construct two-dimensional (2D) structures comprising DNA crystals with covalently bonded metallic nanoparticles, which represent integrated nanocomponents. Our approach exploits the work of Liu et al. (1999) in which 2D DNA crystals with modified surface features were constructed by tiling together rigid DNA motifs composed of double-crossover (DX) molecules containing DNA hairpins (Liu et al., 1999; Winfree et al., 1998). The use of 2D DNA crystals as a scaffolding potentially offers fundamental advantages over other self-assembly approaches with regard to the precision, rigidity, and programmabilty of the assembled nanostructures. On the other hand, this approach presents significant challenges because the unusual DNA motifs employed for DNA tiling appear to require aqueous environments containing significant concentrations of multivalent cations. These conditions are far from those commonly used when dealing with the components of potential interest for nanoelectronic applications, such as metallic nanoparticles and carbon nanotubes. 2D DNA crystals were formed by the assembly of a set of 22 specifically designed synthetic oligonucleotides in solution. The strands form four types of DX molecules, referred to as A, B, C, D in Figure 1. Molecules B and D are designed to have structural features protruding perpendicular to the crystal plane. In our approach, one of the protruding structures in the