Under existing silicon-based computer chip technology, the number of transistors on a chip has doubled about every 18 months according to Moore's law. This pace is likely to slow considerably because of physical and atomic constraints on silicon chips. For instance, the wire components used in silicon chips cannot be made smaller than 300 nm due to the wavelength of light used in lithography. (Hainfeld, 2001). Enlarging silicon computer chips will accommodate greater processing power. Yet in personal computing applications, silicon chips can only be enlarged so much, especially in the context of laptop computers. Additionally, there is a need to for small powerful chips to be used in cellular phones, PDAs, and other handheld devices. Transistors can be made smaller if they are made from nanowires having a diameter of less than 10 nm. Use of these smaller transistors could dramatically increase the number of transistors per area of the chip, allowing computer chips to become smaller and more powerful.
DNA may be used create nanowires because it is sufficiently small and can be made or fashioned as elongate filaments. Double-stranded DNA has a width of approximately 2 nm and each base pair adds approximately 0.34 nm in length to the molecule. Recently, double-stranded DNA has been shown to conduct electricity. (Porath et al. 2000) The conductive ability of DNA may be as good as that of a semiconductor. (Fink and Shonenberger, 1999).
Further, the conductivity of a DNA strand may be enhanced in a variety of ways. In one approach, the filament is doped with metal ions, such as Zn, Co, Ni. With sufficient doping, the conductivity of the filament may be enhanced several orders of magnitude. Alternatively, nucleic acid filaments may be coated with a conductive film, such as a gold or silver film applied by metal atom deposition of other coating methods (Braun 1998 and Richter 2001). Another exemplary DNA nanowire may be created by binding gold to a DNA filament. (Hainfeld, 2001) This is further described in US Patent Publications 2006/0154380 and 2002/0016306, which are hereby incorporated by reference. DNA filaments may be connected to other circuit elements by hybridization with a single-stranded DNA sequence, using standard DNA splicing and ligation methods. (Hainfeld, 2001). Other circuit elements include other DNA nanowires or solid-state circuit elements that are covalently bound to a single-stranded DNA molecule.
Each DNA strand that comprises a nanowire may be made using a commercially available polynucleotide synthesizer, yet this approach is suboptimal. The maximum length of a DNA that can be feasibly made using this technique is 100 base pairs. Furthermore, DNA synthesizers will contain shorter DNA strands as impurities. Alternatively, the DNA used to make a nanowire can be assembled from smaller pure oligonucleotides.
It would therefore be desirable to provide oligonucleotides that can be easily synthesized in bulk and which can be assembled readily into desired lengths and/or filament bundles.