1. DuPont Central Research and Development, Wilmington, Delaware 19880, USA
2. Department of Chemical Engineering and,
3. Bioengineering Program, Lehigh University, Bethlehem, Pennsylvania 18015, USA

Correspondence to: Ming Zheng¹ Correspondence and requests for materials should be addressed to M.Z. (Email: ming.zheng@usa.dupont.com).

Single-walled carbon nanotubes (SWNTs) are a family of molecules that have the same cylindrical shape but different chiralities¹. Many fundamental studies and technological applications² 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^{3, 4}. 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 10⁶⁰ 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.

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