DNA nanotechnology

Since Watson and Crick’s determination of its structure nearly 50 years ago, DNA has come to fill our lives in many areas, from genetic counseling to forensics, from genomics to gene therapy. These, and other ways in which DNA affects human activities, are related to its function as genetic material, not just our genetic material, but the genetic material of all living organisms. Here, we will ignore DNA’s biological role; rather, we will discuss how the properties that make it so successful in acting as genetic material also make it a convenient and logical molecule to use for constructing new materials on the nanometer scale. The well-known B-DNA double helix is about 20 Å wide, and its helical repeat is 10-10.6 nucleotide pairs for a pitch of 34–36 Å. Thus, constructions made from DNA will have nanoscale features.We are all aware that the DNA found in cells is a double helix consisting of two antiparallel strands held together by specific hydrogen-bonded base pairs; adenine (A) always pairs with thymine (T), and guanine (G) always pairs with cytosine (C). The specificity of this base pairing and the ability to ensure that it occurs in this fashion (and not some other1) is key to the use of DNA in materials applications. The double helical arrangement of the two molecules leads to a linear helix axis, linear not in the geometrical sense of being a straight line, but in the topological sense of being unbranched. Genetic engineers discovered in the 1970s how to splice together pieces of DNA to add new genes to DNA molecules2, and synthetic chemists worked out convenient syntheses for short pieces of DNA (up to ~100–150 units) in the 1980s3. Regardless of the impact of these technologies on biological systems, hooking together linear molecules leads only to longer linear molecules, with circles, knots, and catenanes perhaps resulting from time to time.