The assembly of nanostructures according to one's wishes is one great goal of today's materials science. Probably the most promising approach for molecular construction deals with the utilization of DNA-strands that can be combined with atom point precision. Faisal Aldaye and coworkers from the Department of Chemistry, McGill University, Montreal, and the Canadian Institute of Advanced Research, Toronto, have reviewed the various ways in which DNA has been used for nanoscale assembly so far (Science, 321, 1795-1799, 2008). The idea is to create DNA-strands that connect to each other specifically, forming building blocks for macromolecular structures. Most importantly, these DNA parts assemble themselves when brought in proximity with each other – as do many biological structures, such as biomembranes.

In order to manufacture rigid molecular entities, scientists do not combine single DNA-strands but more robust, interconnected double helices, thus producing three basic building blocks: planar tiles formed from various parallel helices, branched junctions, constructed with several DNA arms radiating from a point, and curved helix bundles made from non-coplanar DNA helices. Using these basic units, scientists were able to assemble an impressive variety of DNA constructs. This ranges from simple square grid arrays, actual chains of mechanically interlocked DNA rings, up to three-dimensional DNA cages in the shapes of tetrahedra, cubes, octahedra or even buckyballs. Another intriguing way of shaping DNA are so-called DNA origamis, where computationally designed single strands are continuously folded into desired shape (one example is representing a smiley image).

Besides the astonishing fact of being able to shape molecules more or less arbitrarily, these accomplishments promise much more important applications in biotechnology and nanotechnology: DNA can be combined with other organic or inorganic components, as used in supramolecular chemistry, e.g. photoactive, redox active or magnetic molecules. Consequently, researchers picture the organization quite complex structures, such as artificial photosystems. “The question is, can DNA be used as a positioning molecule to create such arrays that can convert solar to electrical energy?” asks Hanadi Sleiman, the corresponding author. Other possible applications are protein “enzyme factories”, DNA arrays as templates, models for single electron transport etc. “One can imagine the use of DNA capsules as vehicles for the delivery of drugs on demand,” explains Sleiman, “and similarly, if we learn to increase complexity in the DNA-patterns, then we might, one day, assemble a functioning nano-, rather than microelectronic circuit.” At any rate, Watson and Crick would never have guessed that our genetic material would be used as building blocks for molecular machinery!