Research by recent UALR Ph.D. graduate Xiaomin “Helen” Tu is the focus of a recent article in Chemical and Engineering News. The article focuses on research she is doing for DuPont Central Research and Development on single-walled carbon nanotubes and their promise as components in nanoscale electronic devices.

Zheng is working with a team of scientists and researchers to find ways the unique molecular properties of DNA can be exploited to sort single-walled structures so they will have the same physicochemical properties.

Single-walled carbon nanotubes (SWNTs) show great promise as components of nanoscale electronic devices, but most commercial applications have been stymied by the difficulty in isolating nanotubes of identical spiral shapes – or chirials – from a synthetic mixture. Being able to sort the tubes by shape makes the tubes have the same physicochemical properties.

Tu and co-researcher Ming Zheng of DuPont Central Research & Development, together with Suresh Manohar and Anand Jagota of Lehigh University, have shown that the unique molecular properties of DNA can be exploited to sort the tubes.

SWNT synthesis produces a mixture of nanotubes with non-uniform diameters and chirials and, therefore, heterogeneous physicochemical properties. Having previously shown that a particular DNA sequence could form an ordered structure on SWNTs, Zheng and colleagues reasoned that they might be able to find a DNA sequence to purify each type of SWNT in a synthetic mixture. The problem was identifying the correct DNA molecules among an unfeasibly large number of possible 30-nucleotide sequences.

To reduce the DNA library to a more manageable size, the researchers devised a sequence-pattern-expansion scheme that considered all possible DNA sequences. The study yielded more than 20 sequences that could together purify all 12 major chirial semiconducting SWNTs.

The ordered structure minimizes interactions with the ion-exchange chromatography resin and causes early elution.

“This is a very impressive study that reports the most selective method yet found for isolating specific structural forms of SWNTs from mixed samples,” R. Bruce Weisman of Rice University says. “The main limitation is the small scale and high expense.”