Diameter-selective separation of double-walled carbon nanotubes

Abstract

Here, we report a simple and effective way of separating double-walled carbon nanotubes as a function of their diameter using individually dispersed nanotube solutions with the aid of long and random single-stranded DNA. The subtle pH change in nanotube solutions gives rise to the preferential coagulation of large-diameter tubes and allows the easy preparation of small-diameter tubes. The stronger van der Waals forces between large-diameter tubes, combined with the decreased solubility of DNA in water at low pH, lead to the preferential agglomeration of large-diameter tubes. © 2008 American Institute of Physics. ͓DOI: 10.1063/1.3039790͔Carbon nanotubes have attracted the attention of scientists as they are considered to be ideal macromolecules exhibiting unique physical and chemical properties that are useful for various potential applications. Since all known synthetic routes for producing nanotubes yield samples containing mixtures of carbon nanotubes with different diameters and chiralities, extensive efforts have been devoted to finding an effective way of producing or isolating particular types of carbon nanotubes. It has been reported that singlewalled carbon nanotubes ͑SWNTs͒ can be effectively sorted using surfactants in conjunction with multiple density gradient ultracentrifuges 1 or by using aromatic polymers. 2 Very recently, LeMieux et al. 3 reported the efficient fabrication of self-sorted and self-assembled SWNT networks for thin-film transistors through the selective deposition of metallic and semiconducting tubes on the controlled surface of a wafer. DNA has also been used as an effective dispersion and separation agent for SWNTs in water on the basis of its ability to wrap itself around the sidewall of carbon nanotubes due to van der Waals attraction between the DNA molecule and the carbon nanotubes. 4,5 Thus, both theoretical and experimental studies have been carried out in order to understand the nature of the interaction between DNA and nanotubes. [6][7][8][9] On the other hand, double-walled carbon nanotubes ͑DWNTs͒ have attracted considerable attention since their intrinsic coaxial structure gives rise to intriguing electronic and optical properties. 10 In addition, these double-walled tubes possess clear advantages over SWNTs for various specific applications such as superior mechanical properties and structural and thermal stability. 11 In the present paper, we present the development, with the aid of optical spectroscopy, of an efficient method for the separation of DWNTs ͑as a function of their diameter͒ by dispersing the DWNTs in solutions of long and random single-stranded DNA ͑ssDNA͒ sequences. The subtle pH change in the DNA/DWNT solutions gives rise to the preferential coagulation of largediameter tubes and allows the easy precipitation of the smalldiameter DWNTs. In addition, flocculated large-diameter tubes can be separated at low pH by using a mild centrifuge and then easily redispersed in a stock DNA solution with a simple vortex mixer. We have found that this separation tech...

Hybrids of Nucleic Acids and Carbon Nanotubes for Nanobiotechnology

“…Hughes et al used PL to compare 15-m of A, G, C, and T [ 68 ]. Figure 3 shows the changes in PL spectra due to solvent pH that were reported by Kim et al [ 89 ]. Such phenomena are expected to apply to optical switches.…”

“…Currently, the chirality of SWNTs cannot be well controlled during synthesis. A technique for separating SWNTs is one of the major aims of CNT research [ 62 , 84 , 85 , 86 , 87 , 88 , 89 , 90 , 91 , 92 , 93 ]. For example, Vetcher et al separated DNA/RNA-SWNT hybrids using agarose gel electrophoresis [ 84 ].…”

“…Although most separation studies focus on hybrids of SWNTs, Kim et al reported DWNT hybrids as a function of nanotube diameter, suggesting that stronger van der Waals forces between large-diameter tubes were an important factor [ 89 ]. Shakhmaeva et al proposed a unique method of removing DNA molecules from CNT surfaces.…”

“… Differences in photoluminescence (PL) maps due to the pH values of solvents indicated by Kim et al (Reprinted from reference [ 89 ] with permission). …”

PH-sensitive dispersion of carbon nanotubes by myoglobin

“…The other is the non-covalent modification, which does not disrupt CNTs' electronic structures and thus guarantee the original properties intact. 6,7 Protein is a common choice to disperse CNTs in aqueous solution because of its inherent hydrophobic domain and water solubility. Myoglobin, which consists of a single polypeptide chain, is one of the best water -soluble proteins.…”