Free-standing nanoparticle superlattice sheets controlled by DNA

Free-standing nanoparticle superlattices (suspended highly ordered nanoparticle arrays) are ideal for designing metamaterials and nanodevices free of substrate-induced electromagnetic interference. Here, we report on the first DNA-based route towards monolayered free-standing nanoparticle superlattices. In an unconventional way, DNA was used as a ‘dry ligand’ in a microhole-confined, drying-mediated self-assembly process. Without the requirement of specific Watson–Crick base-pairing, we obtained discrete, free-standing superlattice sheets in which both structure (inter-particle spacings) and functional properties (plasmonic and mechanical) can be rationally controlled by adjusting DNA length. In particular, the edge-to-edge inter-particle spacing for monolayered superlattice sheets can be tuned up to 20 nm, which is a much wider range than has been achieved with alkyl molecular ligands. Our method opens a simple yet efficient avenue towards the assembly of artificial nanoparticle solids in their ultimate thickness limit—a promising step that may enable the integration of free-standing superlattices into solid-state nanodevices. Free-standing nanoparticle superlattices offer interesting possibilities for the design of devices free from undesired effects of substrates. DNA can now be used to obtain superlattices with control over interparticle spacing, offering an alternative perspective on the synthesis of nanoparticle solids.