Alexander E. Ribbe

Conformational flexibility facilitates self-assembly of complex DNA nanostructures

Molecular self-assembly is a promising approach to the preparation of nanostructures. DNA, in particular, shows great potential to be a superb molecular system. Synthetic DNA molecules have been programmed to assemble into a wide range of nanostructures. It is generally believed that rigidities of DNA nanomotifs (tiles) are essential for programmable self-assembly of well defined nanostructures. Recently, we have shown that adequate conformational flexibility could be exploited for assembling 3D objects, including tetrahedra, dodecahedra, and buckyballs, out of DNA three-point star motifs. In the current study, we have integrated tensegrity principle into this concept to assemble well defined, complex nanostructures in both 2D and 3D. A symmetric five-point-star motif (tile) has been designed to assemble into icosahedra or large nanocages depending on the concentration and flexibility of the DNA tiles. In both cases, the DNA tiles exhibit significant flexibilities and undergo substantial conformational changes, either symmetrically bending out of the plane or asymmetrically bending in the plane. In contrast to the complicated natures of the assembled structures, the approach presented here is simple and only requires three different component DNA strands. These results demonstrate that conformational flexibility could be explored to generate complex DNA nanostructures. The basic concept might be further extended to other biomacromolecular systems, such as RNA and proteins.

Surface-Mediated DNA Self-Assembly

This communication reports a strategy for solid surface-mediated DNA self-assembly. DNA molecules weakly interact with solid surfaces; thus are confined to solid surfaces. The confinement reduces the flexibility of DNA nanomotifs and promotes the DNA 2D crystals to grow on solid surfaces. As a demonstration, periodic DNA nanoarrays have been directly assembled onto mica surfaces. Such in situ assembly eliminates the sample transfer process between assembly and characterization and possible applications.

Symmetry Controls the Face Geometry of DNA Polyhedra

Two complementary strategies have been developed to control the face geometry during the self-assembly of DNA polyhedra from branched DNA nanomotifs (tiles). In these approaches, any two interacting tiles are not equivalent in terms of either sequence or orientation; thus, each face must contain an even number of tiles. As a demonstration, DNA cubes, whose each face contains four tiles, have been assembled through these approaches.

Synergistic self-assembly of RNA and DNA molecules

DNA has recently been used as a programmable ‘smart’ building block for the assembly of a wide range of nanostructures. It remains difficult, however, to construct DNA assemblies that are also functional. Incorporating RNA is a promising strategy to circumvent this issue as RNA is structurally related to DNA but exhibits rich chemical, structural and functional diversities. However, only a few examples of rationally designed RNA structures have been reported. Herein, we describe a simple, general strategy for the de novo design of nanostructures in which the self-assembly of RNA strands is programmed by DNA strands. To demonstrate the versatility of this approach, we have designed and constructed three different RNA–DNA hybrid branched nanomotifs (tiles), which readily assemble into one-dimensional nanofibres, extended two-dimensional arrays and a discrete three-dimensional object. The current strategy could enable the integration of the precise programmability of DNA with the rich functionality of RNA.

Multifunctional nanoparticle-loaded spherical and wormlike micelles formed by interfacial instabilities.

Hybrid spherical and wormlike amphiphilic block copolymer micelles are formed through evaporation-induced interfacial instabilities of emulsion droplets, allowing the incorporation of pre-synthesized hydrophobic inorganic nanoparticles within the micelle cores, as well as co-encapsulation of different nanoparticles. This encapsulation behavior is largely insensitive to particle surface chemistry, shape, and size, thus providing a versatile route to fabricate multifunctional micelles.

DNA self-assembly: from 2D to 3D

This paper describes our recent efforts on the self-assembly of three-dimensional (3D) DNA nanostructures from DNA star motifs (tiles). DNA star motifs are a family of DNA nanostructures with 3, 4, 5, or 6 branches; they are named as 3-, 4-, 5-, 6-point-star motifs, respectively. Such motifs are programmed to further assemble into nanocages (regular polyhedra or irregular nanocapsules) with diameters ranging from 20 nm to 2 microm. Among them, DNA nanocages derived from 3-point-star motif consists of a group of regular polyhedra: tetrahedra, hexahedra (or cubes), dodecahedra and buckyballs (containing 4, 8, 20, and 60 units of the 3-point-star motif, respectively). An icosahedron consists of twelve 5-point-star motifs and is similar to the shapes of spherical viruses. 6-point-star motifs can not assemble into regular polyhedra; instead, some sphere-like or irregular cages with diameters about 1-2 microm will form. Similar large cages can also assemble from the 5-point-star motif when the DNA concentrations are higher than those for assembling regular icosahedra. In our study, we have identified several important factors for assembly of well-defined 3D nanostructures, including the concentration, the flexibility, and the arm length of the DNA tiles and the association strength between the DNA tiles.

DNA-Templated Fabrication of Two-Dimensional Metallic Nanostructures by Thermal Evaporation Coating

A biotemplating strategy for fabrication of metallic nanoparticle arrays has been developed. The templates are self-assembled DNA nanostructures, which dictate nanoparticle synthesis in the gas-solid phase (during thermal evaporation).

Templated Self-Assembly of a Covalent Polymer Network for Intracellular Protein Delivery and Traceless Release

Trafficking proteins inside cells is an emerging field with potential utility in basic cell biology and biological therapeutics. A robust and sustainable delivery strategy demands not only good protection of the cargo but also reversibility in conjugation and activity. We report a protein-templated polymer self-assembly strategy for forming a sheath around the proteins and then tracelessly releasing them in the cytosol. The versatility of the approach, demonstrated here, suggests that the strategy is compatible with a wide array of biologics.

Smart Organic Two‐Dimensional Materials Based on a Rational Combination of Non‐covalent Interactions

Rational design of organic 2D (O2D) materials has made some progress, but it is still in its infancy. A class of self-assembling small molecules is presented that form nano/microscale supramolecular 2D materials in aqueous media. A judicial combination of four different intermolecular interactions forms the basis for the robust formation of these ultrathin assemblies. These assemblies can be programmed to disassemble in response to a specific protein and release its non-covalently bound guest molecules.

Rapid, Large-Area Synthesis of Hierarchical Nanoporous Silica Hybrid Films on Flexible Substrates

We report a simple strategy for the creation of large-area nanoporous hybrid films of silica, carbon, and gold on polyethylene terephthalate via photothermal processing. This method enables the selective heating of light-absorbing thin films on low-temperature substrates using sub-millisecond light pulses generated by a xenon flash lamp. The film contains gold nanoparticles as the nanoheaters to convert light energy to heat, a sacrificial block copolymer surfactant to generate mesopores, and cross-linked polyhedral oligomeric silsesquioxane as the silica source to form the skeleton of the porous structure. Hierarchical porous structures are achieved in the films after photothermal treatment, with uniform mesopores (44-48 nm) on the surface and interconnected macropores (>50 nm) underneath resulting from a foaming effect during release of gaseous decomposition products. The loading of gold nanoparticles is up to 43 wt % in the product, with less than 2 wt % organic residue. This rapid and large-area process for the synthetis of porous structures is compatible with roll-to-roll manufacturing for the fabrication of flexible devices.