DNA and conducting electrons

How do electrons behave in a DNA molecule? Are they all involved in more or less localized bonds, be it covalent or hydrogen-bridge bonds, or are there also free electrons present in the molecule? If so, can one take advantage of these mobile charge carriers confined to the elongated shape of the DNA molecule, which would then define a one-dimensional electrical conductor? These are the questions that this article will try to reflect on. Despite the fact that the chemistry of the DNA molecule happens to be extremely well understood, it has only recently been considered as a possible candidate for molecular wires. This might mainly be due to the fact that individual DNA molecules are much more difficult to observe than microscopic metal structures or carbon nanotubes: those can readily be visualized in conventional electron microscopes. Whereas chemists have developed a variety of tools and methods to precisely characterize and control an ensemble of DNA molecules, experiments on individual species require new approaches for visualization and manipulation on a molecular scale. However, once the technology to image and manipulate individual molecules is readily available, the prospects of employing DNA as molecular wires are truly exciting. A great number of catalytic reactions, carried out by enzymes, are well known. They allow for multiplying, cutting and joining the DNA molecules. Length determinations on a large ensemble of molecules can be done by electrophoresis techniques. Filtering techniques are at hand to achieve monodisperse molecules at almost any desired length from a few nucleotides to macroscopic length scales. It is even feasible to design and construct twoas well as three-dimensional geometrical objects made up of DNA molecules [1]. Last, but not least, the DNA is soluble in water, and methods have been developed to stretch out long DNA molecules on various surfaces, including those of silicon wafers [2]. All this would, at least in principle, allow interfacing these biomolecules in a highly parallel fashion to structures produced by silicon technology. Provided the DNA is capable of carrying out electronic functions, this could be the beginning of a development that might lead to integrated DNA-based electronic devices.