Channels from DNA: Artificial transmembrane channels are of interest for applications, such as sensing and modifying cell signaling. Langecker et al. (p. 932 ; see the Perspective by Strano ) used α-hemolysin as a model for creating a nanostructure with DNA origami that, when inserted into a lipid bilayer membrane, acted as a membrane channel. Ion channel responses were similar to those measured for natural ion channels, and channels that protruded further into the membrane exhibited greater gating responses. The channels were used to detect single-DNA molecules.

Reconfigurable DNA structures: DNA origami—nanostructures created by programming the assembly of single-stranded DNA through base pairing—can create intricate structures. However, such structures lack the flexible and reversible interactions more typical of biomolecular recognition. Gerling et al. created three-dimensional DNA nanostructures that assemble though nucleotide base-stacking interactions (see the Perspective by Shih). These structures cycled from open to closed states with changes in salt concentration or temperature. Science, this issue p. 1446 ; see also p. 1417

DNA nanotechnology enables the programmed synthesis of intricate nanometer-scale structures for diverse applications in materials and biological science. Precise control over the 3D solution shape and mechanical flexibility of target designs is important to achieve desired functionality. Because experimental validation of designed nanostructures is time-consuming and cost-intensive, predictive physical models of nanostructure shape and flexibility have the capacity to enhance dramatically the design process. Here, we significantly extend and experimentally validate a computational modeling framework for DNA origami previously presented as CanDo [Castro,C.E., Kilchherr,F., Kim,D.-N., Shiao,E.L., Wauer,T., Wortmann,P., Bathe,M., Dietz,H. (2011) A primer to scaffolded DNA origami. Nat. Meth., 8, 221–229.]. 3D solution shape and flexibility are predicted from basepair connectivity maps now accounting for nicks in the DNA double helix, entropic elasticity of single-stranded DNA, and distant crossovers required to model wireframe structures, in addition to previous modeling (Castro,C.E., et al.) that accounted only for the canonical twist, bend and stretch stiffness of double-helical DNA domains. Systematic experimental validation of nanostructure flexibility mediated by internal crossover density probed using a 32-helix DNA bundle demonstrates for the first time that our model not only predicts the 3D solution shape of complex DNA nanostructures but also their mechanical flexibility. Thus, our model represents an important advance in the quantitative understanding of DNA-based nanostructure shape and flexibility, and we anticipate that this model will increase significantly the number and variety of synthetic nanostructures designed using nucleic acids.

Site-specific ultraviolet “point welding” makes designed DNA objects much more durable.

Speeding Up Nanoscale DNA Assembly: An impressive array of three-dimensional (3D) nanoscale objects has been assembled by folding a long, single-stranded DNA scaffold by binding of short DNA staples. However, these processes tend to be slow and inefficient. Sobczak et al. (p. 1458 ) examined the folding process with an intercalating fluorescence dye to measure the formation of double-stranded DNA in folding processes or single-stranded DNA in unfolding. Reaction conditions were identified that sped up folding by orders of magnitude and increased yields of the 3D nanoscale objects to nearly 100%.

DNA has become a prime material for assembling complex three‐dimensional objects that promise utility in various areas of application. However, achieving user‐defined goals with DNA objects has been hampered by the difficulty to prepare them at arbitrary concentrations and in user‐defined solution conditions. Here, we describe a method that solves this problem. The method is based on poly(ethylene glycol)‐induced depletion of species with high molecular weight. We demonstrate that our method is applicable to a wide spectrum of DNA shapes and that it achieves excellent recovery yields of target objects up to 97 %, while providing efficient separation from non‐integrated DNA strands. DNA objects may be prepared at concentrations up to the limit of solubility, including the possibility for bringing DNA objects into a solid phase. Due to the fidelity and simplicity of our method we anticipate that it will help to catalyze the development of new types of applications that use self‐assembled DNA objects.