Nanotube-Sorting Method Could Pave the Way for Medical Applications

Originally Published MDDI February 2004

R&D DIGEST

Erik Swain

A group of scientists has found a way to sort carbon nanotubes through the use of DNA. Such tubes form the basis of building blocks for medical diagnostic devices and other electronic applications that are more than 100 times smaller than what is found in today's microchips.

The group, led by researchers from DuPont's (Wilmington, DE) Central Research & Development department, found that the ability to sort and assemble carbon nanotubes allows for uniform conductivity, which will make them more useful in practical applications. Normally when nanotubes are fabricated, ones of different electronic types randomly clump together, compromising conductivity.

The researchers first found that single-stranded DNA can react with carbon nanotubes to form stable hybrids that disperse the nanotubes in an aqueous solution. Then, working with scientists from the Massachusetts Institute of Technology (Cambridge, MA) and the University of Illinois (Urbana, IL), they were able to separate the nanotubes using single-stranded DNA and anion-exchange chromatography. 

They found that a particular sequence of the DNA assembled into a helical structure around individual carbon nanotubes. The hybrids can be sorted using anion-exchange chromatography because they have different electrostatic properties depending on the diameter and electronic properties of the nanotubes. 

What this means is that metallic carbon nanotubes can be separated from semiconducting carbon nanotubes, and the latter can be sorted by diameter. Now that the different kinds of nanotubes can be isolated, it may become easier to use them in developing medical applications. The group published its findings in the journal Science. 

The research team included DuPont's Ming Zheng, Anand Jagota, Bruce A. Diner, Robert S. McLean, G. Bibiana Onoa, Ellen D. Semke, and Dennis J. Walls; MIT's Adelina P. Santos, Grace Chou, Mildred S. Dresselhaus, and Georgii G. Samsonidze; and Illinois's Michael S. Strano, Paul Barone, and Monica Usrey.

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