Constantine Y. Khripin, Nicholas Arnold-Medabalimi, Denis Pristinski, and Ming Zheng

The DNA dispersion of single - walled carbon nanotubes, forming the hybrid nanoparticle DNA-SWCNT, has seen extensive use as a convenient way of purifying and processing carbon nanotubes. We are investigating molecular self-assembly as a new way of purifying DNA-SWNT, as well as for probing the structure of the hybrid. We find that the addition of PEG induces DNA-SWNT assembly into a gel – like phase. This is similar to the PEG “molecular crowding” induced transition of double-stranded DNA into a condensed phase. As with DNA, DNA-SWNT condensation is length dependent; AFM measurements show both long and short nanotubes can be isolated, e.g. 460±180 nm and 160±50 nm. Dynamic light scattering and UV-VIS data show that this method removes non-SWNT impurities present in the suspension. We also show that “molecular crowding” by PEG can induce DNA-SWNT self-assembly into a 2D nematic phase on a substrate. Because this phase appears to be very stable, we are exploring its use for nanotube characterization by scanning probe microscopy, to examine the structure of DNA on the nanotube surface.