DNA sequence motifs for structure-specific recognition and separation of carbon nanotubes

Abstract

Single-walled carbon nanotubes (SWNTs) are a family of molecules that have the same cylindrical shape but different chiralities. Many fundamental studies and technological applications of SWNTs require a population of tubes with identical chirality that current syntheses cannot provide. The SWNT sorting problem-that is, separation of a synthetic mixture of tubes into individual single-chirality components-has attracted considerable attention in recent years. Intense efforts so far have focused largely on, and resulted in solutions for, a weaker version of the sorting problem: metal/semiconductor separation. A systematic and general method to purify each and every single-chirality species of the same electronic type from the synthetic mixture of SWNTs is highly desirable, but the task has proven to be insurmountable to date. Here we report such a method, which allows purification of all 12 major single-chirality semiconducting species from a synthetic mixture, with sufficient yield for both fundamental studies and application development. We have designed an effective search of a DNA library of approximately 10(60) in size, and have identified more than 20 short DNA sequences, each of which recognizes and enables chromatographic purification of a particular nanotube species from the synthetic mixture. Recognition sequences exhibit a periodic purine-pyrimidines pattern, which can undergo hydrogen-bonding to form a two-dimensional sheet, and fold selectively on nanotubes into a well-ordered three-dimensional barrel. We propose that the ordered two-dimensional sheet and three-dimensional barrel provide the structural basis for the observed DNA recognition of SWNTs.

Chirality-controlled synthesis of single-wall carbon nanotubes using vapour-phase epitaxy

“…The chirality-pure (7,6), (6,5) and (7, 7) nanotube seeds were obtained using the DNA-based chromatographic purification 12,26 . Seed solutions with a concentration of B0.5 mg ml À 1 were drop-deposited onto quartz or Si/SiO 2 substrates and incubated for 30 min to 1 week, followed by gentle rinse with water and blow-dry.…”

“…As the electronic property of an SWCNT strongly depends on its chirality, the lack of synthetic control in chirality has long been recognized as a fundamental impediment in the science and application of SWCNTs. Previous efforts to address this issue have resulted in significant progress in separation of synthetic mixtures, yielding predominantly single-chirality nanotube species [11][12][13][14][15] . However, separation processes are limited by their small scale, high cost and short length (o500 nm) of the resulting chirality-pure nanotubes.…”

“…Our strategy is to combine nanotube separation with synthesis to achieve controlled growth of nanotubes with preselected chirality. Tremendous progress has been made in recent years in SWCNT separation [11][12][13][14][15]25,26 . In particular, DNA-based chromatographic separation allows purification of both semiconducting and metallic single-chirality SWCNTs through the use of different DNA sequences 12,26 .…”

“…Tremendous progress has been made in recent years in SWCNT separation [11][12][13][14][15]25,26 . In particular, DNA-based chromatographic separation allows purification of both semiconducting and metallic single-chirality SWCNTs through the use of different DNA sequences 12,26 . In this work, three exemplary chirality-pure (7,6), (6,5) and (7,7) SWCNT seeds with purity up to 90% are used.…”

Nanotubes keep rolling on

“…6 and page 481 of this issue). Although not fully understood, this approach is thought to involve the DNA strands forming two-dimensional sheets, held together by hydrogen bonds, which then fold around and bind to the target nanotubes to form three-dimensional barrels.…”