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DNA Nanotubes

Made almost entirely of DNA, tubes might be useful for gene therapy

by Stu Borman
June 6, 2005 | A version of this story appeared in Volume 83, Issue 23

Cross-sectional view of DNA nanotube with exploded view of nanotube wall.
Cross-sectional view of DNA nanotube with exploded view of nanotube wall.


The first layered nanotubes composed almost entirely of DNA have been created. Layers of DNA in the nanotubes are held together by hybridization of a series of DNA strands. The nanotubes fall apart when heated, releasing single-stranded DNA.

The nanotubes were synthesized and characterized by chemistry professor Charles R. Martin and coworkers Shifeng Hou and Jiahai Wang at the University of Florida, Gainesville (J. Am. Chem. Soc., published online May 25, "These nanotubes might prove to be the ultimate DNA delivery vehicles--for treatment of genetic-based disorders, for example--because the nanotubes are essentially all DNA," Martin says.

The DNA nanotubes are constructed in the 100-nm-diameter pores of alumina membranes. A diorganophosphonate "skin" is deposited in the pores, and Zr(IV) is used to link the diorganophosphonates to phosphonate groups on the end of a single-stranded DNA strand. The strand's sequence is partially complementary to that of a second single-stranded DNA, and thus the two strands can hybridize. Similarly, the second DNA strand hybridizes with a third DNA strand. The resulting cylindrical assemblies--three layers of DNA plus the linkers and skin--are then released by dissolution of the template, yielding nanotubes made almost entirely of DNA.

The paper focuses primarily on nanotubes made from 15-base DNA strands, but Martin and coworkers also can prepare nanotubes from 8- and 12-base DNAs. "The DNA molecules composing these tubes can be varied at will," they note.

"I have not seen similar approaches based on template construction of DNA nanotubes in which the DNA can eventually be liberated from the support," comments associate researcher Alberto Bianco of the Institute of Molecular & Cellular Biology at the French National Center for Scientific Research in Strasbourg.

In previous work, researchers have made DNA-containing nanotubes by depositing DNA on a substrate and then functionalizing the DNA in various ways. But in the new nanotubes, the DNA content is more predominant, and Martin's approach "allows better control of the DNA nanotube structure," says Bianco, whose research interests include carbon nanotube biofunctionalization.

The new nanotubes "could act as vehicles to deliver the DNA of which they are composed," Bianco says. "In general, DNA does not cross cell membranes easily, and as a result, rates of transfection [incorporation of DNA into genes] are very low. Methods to improve transfection are based on the formation of complexes between DNA and suitable carriers, such as liposomes, dendrimers, cationic polymers, and, more recently, carbon nanotubes."

The new DNA nanotubes could make it possible to transfer DNA without separate carriers, but this would necessitate "that these tubes are able to cross the cell membrane and reach the nucleus," which has yet to be demonstrated, Bianco notes.



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