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DNA Nanowires
James F. Hainfeld*, Frederic R. Furuya**, Richard D. Powell**, and Wenqiu Liu**
*Biology Department, Brookhaven National Lab., Upton, NY 11973
**Nanoprobes, Incorporated, 95 Horseblock Road, Yaphank, NY 11980
A wire width 2 nm may be achieved by placing gold quantum dots along a DNA template. Ends of the DNA-nanowire may be designed with sequences to attach by hybridization to complementary sequences on target connection pads, so that the two ends will seek and automatically wire correctly in solution. This strategy is easily adaptable to 3-dimensional wiring. Conduction between gold quantum dots may be studied as a function of spacing, size and coatings. In addition, the gold dots catalyze additional metal deposition leading to continuous metal nanowires. Preliminary results have demonstrated high loading of DNA strands with 1.4 nm Nanogold clusters spaced ~2 nm apart, showing basic feasibility.
DNA is close to an ideal wire template since it is of narrow diameter (2 nm), is flexible, can be targeted uniquely at both ends, and also has the property that its length can be exactly controlled by its production by DNA synthesizer or enzymes following a template. This is in contrast to other polymers and nanotubes whose lengths are poorly controlled and with nanotubes, have restricted flexibility.
Close packing of nanowires may require insulation. This may be achieved by several methods: 1) surface oxidation; 2) reaction with silanes to form a glass; or 3) coating with alkane thiols. All of these form insulating coatings and have been demonstrated for metal surfaces and are applicable to the DNA nanowires.
Double stranded DNA (from T7 bacteriophage) was labeled with 1.4 nm Nanogold clusters, and examined in the Brookhaven STEM (Scanning Transmission Electron Microscope); see Fig. 1. The average spacing between gold clusters was ~2 nm. This is of interest since the distance for tunneling of electrons between metal particles is also about 2 nm. Although a variety of methods are possible to link gold clusters to nucleic acids, including covalent attachment, photoreaction, intercalation, the method chosen here was to use positively charged Nanogold binding to the negatively charged DNA.
Metallographic methods have been developed to specifically deposit additional metal on the small gold clusters, and their enlargement can be followed by electron microscopy. Confluency between neighboring clusters could be achieved (Fig. 2). Here, gold was deposited catalytically, but silver and other metals have also been used in a similar process. In this way, continuous solid metal wires may be constructed.
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Fig. 1 (Left): 1.4 nm gold clusters (bright spots) bound to double stranded bacteriophage T7 DNA (rope-like strands). Dark field, unstained STEM image on a thin carbon substrate. Full width 128 nm.
Fig. 2 (Right): Nanogold clusters nucleating further gold deposition so that they become contiguous. Metal deposition was then stopped at various times to demonstrate growth of cluster size. Top image after 5 min, bottom after 10 min. BNL STEM micrograph, darkfield, elastically scattered signal; full width of each image 230 nm.
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