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Posted: Aug 31, 2006

DNA as template for assembling nanostructures

(Nanowerk Spotlight) Recent developments in DNA-based nanotechnology have shown the suitability of this novel assembly method for constructing useful nanostructures. DNA molecules can serve as precisely controllable and programmable scaffolds for organizing functional nanomaterials in the design, fabrication, and characterization of nanometer scale electronic devices and sensors. DNA-templated metallic nanowires are such an example and over the past few years DNA scaffolds have been metallized with silver, gold, palladium, platinum and copper. DNA-based fabrication methods could ultimately lead to naturally bio-compatible nanodevices.
Recent research at Duke University optimized the fabrication of DNA-templated silver nanowires while also performing electrical analysis of the resulting wires.
Dr. Sung Ha Park explained the recent work to Nanowerk: "For the past few decades, direct electrical transport measurement in DNA molecules has been considered an interesting research subject. Even though some conductivity experiments with DNA have shown semiconducting or superconducting behavior at extreme conditions, other studies have concluded that DNA molecules are insulators. Rather than relying on electrical transport through DNA itself, we have made use of DNA nanostructures as templates for the specific deposition of functionalized metallic silver nanowires."
Park, now a postdoc at Caltech's DNA and Natural Algorithms Group, is first author of a recent paper titled "Optimized fabrication and electrical analysis of silver nanowires templated on DNA molecules" published in the July 17, 2006 edition of Applied Physics Letters. Park worked on the paper while a grad student at Duke University working with professors Gleb Finkelstein and Thomas LaBean.
In their paper, the researchers describe the fabrication of silver nanowires templated on both synthetic double-stranded DNA and native bacteriophage λ-DNA molecules. After a chemical silver deposition, the metallized DNA wires have a diameter down to 15 nm and are among the thinnest metallic nanowires available to date.
Park and his colleagues also demonstrate the electrical conductivity of their metallized nanowires. Two-terminal current-voltage measurements of about 70 silver wires have demonstrated various conduction behaviors: about 45% were highly conducting, ∼15% nonohmic-semiconducting, and ∼40% showed insulting characteristics.
SEM images of λ- (left) and synthetic double-stranded DNA (right) after two-step silver metallization process. (Reprinted with permission from the American Institute of Physics)
Park explains that understanding of the mechanism limiting the preinitialized conductance of the wires is necessary before these DNA templated wires can be reliably used as interconnects in bioelectronic nanodevices.
"While non-metallized DNA molecules do not appear to be highly conductive, the DNA templated metallic nanowires promise to become useful as programmable interconnects in bioelectronic devices" says Park.
The advantages of DNA-templated fabrication of electro-mechanically functionalized devices such as metallic nanowires and magnetic quantum dot arrays – 'site-specific' alignment and molecular lithography – could become a very interesting aspect for future nanoelectronics applications.
Finkelstein notes that the wires may be potentially used as interconnects in future bio-nano-devices, compatible with other biochemical fabrication steps. "Eventually" he says, "one may hope making devices that will be naturally bio-compatible."
Another potential future application Finkelstein and his group are already working on is templating Single-Electron Transistors (SETs) on DNA scaffolds where the metalized DNA wires may be used as leads for the SETs. This represents the first important step in their implementation. "Given the small size and great complexity of the modern electronic chips, the alternative, potentially competitive fabrication strategies should rely on bio-chemical self-assembly techniques."
By , Copyright Nanowerk LLC

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