Carbon Nanotube Sorting and Purifying by Ion Exchange Chromatography

Wrapping of carbon tubes by synthetic single-stranded DNA was found that electrostatics of the DNA-CNT hybrid depends on tube diameter and electronic  properties, enabling nanotube separation by anion exchange chromatography. Optical absorption and Raman spectroscopy show that early fractions are enriched in the small diameter and metallic tubes, where late fractions are enriched in the large diameter and semiconducting tubes.  The purification of semiconducting single- walled carbon nanotubes (SWCNT) with a purity of 99% or higher is important in the electronic industry. The purification of semiconducting SWCNT from metallic SWCNT are related to hydrophilic and ligand density of anion exchange packing materials,  column dimension  and DNA-CNT hybrid.

The following are the comparison of conventional NS 1500 column to CNT-NS 1500 column in the separation of single stranded synthetic oligonucleotides standard mixture. Hydrocell CNT-NS 1500 showed the longer and wider retention time in the separation of the same standard sample of 12-18 mer of phosphated oligothymidylic acid in the comparison with conventional NS 1500 for oligonucleotides and DNA fragment purification..  The relationship of DNA-CNT hybrid and the characteristic of  anion exchange packing materials in the purify semiconducting single-walled carbon nanotubes are under investigation.

Conventional Hydrocell NS 1500  Column                      Hydrocell CNT-NS 1500 Column

Column: 7.8 x 75 mm

Mobile Phase:
Eluent A: 25 mM CHES, pH 8.0
Eluent B: Eluent A + 1.2 M Ammonium Sulfate, pH 8.0
Gradient: Linear 10-50% B in 40 minutes
Flow Rate: 2.5 mL / min.
Detection: UV 260 nm
Samples: OLigothymidylic Acid d( pT) 12-18 mer, 5 units in 1 mL of eluent A
Injection: 30 µL

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* Courtesy of Dr. Wei Zhao, Professor ,Department of Chemistry, University of Arkansas

The separation procedure is as follows: 1) 1 mg of HiPco nanotube was suspended in 1 mL aqueous ssDNA (GT)₄₀ solution (1 mg/mL ssDNA, 0.1 M NaCl in H₂O). This mixture was kept in an ice-water bath and sonicated with a sonicator (Sonics, VCX 130PB) for 1 hour at a power level of about 8 W. After sonication, the sample was centrifuged overnight at 14,000 rpm (16,000 g, VWRbrand Galaxy 16 Microcentrifuge) to remove the insoluble materials; 2) A volume of 600 ìL of dispersed carbon nanotubes in ssDNA solution was injected into an anion-exchange column NS 1500 (75 mm by 7.8 mm, Biochrom Labs, Inc.) in the HPLC system, and eluted in a linear salt gradient (0-0.9 M NaSCN in 20 mM MES buffer at pH 7.0) at a flow rate of  2.0 mL/min. Starting from 4 minute of the elution time, fractions were collected in every 15 s.

Reference:

Structure-Based Carbon Nanotube Sorting by Sequence-Dependent DNA Assembly

Ming Zheng,^1* Anand Jagota,¹ Michael S. Strano,² Adelina P. Santos,³ Paul Barone,² S. Grace Chou,³ Bruce A. Diner,¹ Mildred S. Dresselhaus,³ Robert S. Mclean,¹ G. Bibiana Onoa,¹ Georgii G. Samsonidze,³ Ellen D. Semke,¹ Monica Usrey,² Dennis J. Walls¹

Science 28 November 2003: 1545