DNA-Assisted Dispersion of Carbon Nanotubes and Comparison with Other Dispersing Agents

Separation and sorting of pristine carbon nanotubes (CNTs) from bundle geometry is a very challenging task due to the insoluble and nondispersive nature of CNTs in aqueous medium. Recently, many studies have been performed to address this problem using various organic and inorganic solutions, surfactant molecules, and biomolecules as dispersing agents. Recent experimental studies have reported the DNA to be highly efficient in dispersing CNTs from bundle geometry. However, there is no microscopic study and also quantitative estimation of the dispersion efficiency of the DNA. Using all-atom molecular dynamics simulation, we study the structure and stability of single-stranded DNA (ssDNA)-single-walled carbon nanotube (SWNT) (6,5) complex. To quantify the dispersion efficiency of various DNA sequences, we perform potential of mean forces (PMF) calculation between two bare SWNTs as well ssDNA-wrapped CNTs for different base sequences. From the PMF calculation, we find the PMF between two bare (6,5) SWNTs to be approximately -29 kcal/mol. For the ssDNA-wrapped SWNTs, the PMF reduces significantly and becomes repulsive. In the presence of ssDNA of different polynucleotide bases (A, T, G, and C), we present a microscopic picture of the ssDNA-SWNT (6,5) complex and also a quantitative estimate of the interaction strength between nanotubes from PMF calculation. From PMF, we show the sequence of dispersion efficiency for four different nucleic bases to be T > A > C > G. We have also presented a comparison of the dispersion efficiencies of ssDNA, flavin mononucleotide surfactant, and poly(amidoamine) (PAMAM) dendrimer by comparing their respective PMF values.