A DNA nanostructure consisting of four four-arm junctions oriented with a square aspect ratio was designed and constructed. Programmable self-assembly of 4 x 4 tiles resulted in two distinct lattice morphologies: uniform-width nanoribbons and two-dimensional nanogrids, which both display periodic square cavities. Periodic protein arrays were achieved by templated self-assembly of streptavidin onto the DNA nanogrids containing biotinylated oligonucleotides. On the basis of a two-step metallization procedure, the 4 x 4 nanoribbons acted as an excellent scaffold for the production of highly conductive, uniform-width, silver nanowires.

DNA molecules have been used to build a variety of nanoscale structures and devices over the past 30 years, and potential applications have begun to emerge. But the development of more advanced structures and applications will require a number of issues to be addressed, the most significant of which are the high cost of DNA and the high error rate of self-assembly. Here we examine the technical challenges in the field of structural DNA nanotechnology and outline some of the promising applications that could be developed if these hurdles can be overcome. In particular, we highlight the potential use of DNA nanostructures in molecular and cellular biophysics, as biomimetic systems, in energy transfer and photonics, and in diagnostics and therapeutics for human health.

Traditional robots 1 rely on computing to coordinate sensing and actuating components and to store internal representations of their goals and environment. Any implementation of single-molecule based robotics must overcome the limited ability of individual molecules to store complex programs and, for example, use architectures that obtain complex behaviors from the interaction of simple robots with their environment [2][3][4] . Previous research in DNA walkers 5 focused on transitioning from non-autonomous systems 6, 7 to directed but brief motion on one-dimensional tracks8 -11. Herein, we obtain elementary robotic behaviors from the interaction between a random walker incorporating deoxyribozymes 12 and a precisely defined environment. Using singlemolecule microscopies we demonstrate that such walkers achieve directionality by sensing and modifying their environment, following trails of recognition elements ("bread crumbs") laid out on a two-dimensional DNA origami landscape 13 . These molecular robots autonomously carry out sequences of actions such as "start", "follow", "turn", and "stop", thus laying the foundation for the synthesis of more complex robotic behaviors at the molecular level by incorporating additional layers of control mechanisms. For example, interactions between multiple molecular robots could lead to collective behavior14 , 15, while the ability to read and transform secondary cues on the landscape could provide a mechanism for Turing-universal algorithmic behavior2 ,16,17 .Author Contributions: AFM experiments were performed by K.L. (majority), J.N., and N. D.; analysis was performed by N. D., K.L., J.N., S.T., and supervised by E.W., and H.Y. Fluorescence microscopy and particle tracking analysis were performed by A.J.M., N.M., and A.J.B, supervised by N. G. W. Spiders were synthesized, purified, and their integrity confirmed and monitored by S.T. SPR experiments were performed by R. P. Research coordination by M.N.S., material transfer coordination by S.T., J.N., and K.L. Experimental design and manuscript was done with input from all authors. Author Information: Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The authors declare no competing financial interests. Correspondence and requests for materials should be addressed to: mns18@columbia.edu, winfree@caltech.edu, nwalter@umich.edu, hao.yan@asu.edu Supplementary Information is linked to the online version of the paper at www.nature.com/nature. NIH Public Access Author ManuscriptNature. Author manuscript; available in PMC 2010 November 1. Restated in a biochemically more intuitive manner: A deoxyribozyme on a site that was previously converted to a product will dissociate faster, whereas it will stick longer on the substrates and eventually cleave them. Because spiders have multiple legs, a single dissociated leg will quickly reattach to nearby product or substrate. It follows that the body of a spider positioned at the interface between products and substrates will move toward the s...

Scaffolded DNA origami is a versatile means of synthesizing complex molecular architectures. However, the approach is limited by the need to forward-design specific Watson-Crick base-pairing manually for any given target structure. Here, we report a general, top-down strategy to design nearly arbitrary DNA architectures autonomously based only on target shape. Objects are represented as closed surfaces rendered as polyhedral networks of parallel DNA duplexes, which enables complete DNA scaffold routing with a spanning tree algorithm. The asymmetric polymerase chain reaction was applied to produce stable, monodisperse assemblies with custom scaffold length and sequence that are verified structurally in 3D to be high fidelity using single-particle cryo-electron microscopy. Their long-term stability in serum and low-salt buffer confirms their utility for biological as well as nonbiological applications.

Although a multitude of promising anti-cancer drugs have been developed over the past 50 years, effective delivery of the drugs to diseased cells remains a challenge. Recently, nanoparticles have been used as drug delivery vehicles due to their high delivery efficiencies and the possibility to circumvent cellular drug resistance. However, the lack of biocompatibility and inability to engineer spatially addressable surfaces for multi-functional activity remains an obstacle to their widespread use. Here we present a novel drug carrier system based on self-assembled, spatially addressable DNA origami nanostructures that confronts these limitations. Doxorubicin, a well-known anti-cancer drug, was noncovalently attached to DNA origami nanostructures through intercalation. A high level of drug loading efficiency was achieved, and the complex exhibited prominent cytotoxicity not only to regular human breast adenocarcinoma cancer cells (MCF 7), but more importantly to doxorubicin-resistant cancer cells, inducing a remarkable reversal of phenotype resistance. With the DNA origami drug delivery vehicles, the cellular internalization of doxorubicin was increased, which contributed to the significant enhancement of cell-killing activity to doxorubicin-resistant MCF 7 cells. Presumably, the activity of doxorubicin-loaded DNA origami inhibits lysosomal acidification, resulting in cellular redistribution of the drug to action sites. Our results suggest that DNA origami has immense potential as an efficient, biocompatible drug carrier and delivery vehicle in the treatment of cancer.