Dispersion and Exfoliation of Nanotubes with Synthetic Oligonucleotides: Variation of Dispersion Efficiency and Oligo-Nanotube Interaction with Base Type

Single walled carbon nanotubes (SWNTs) were dispersed and exfoliated in four different homopolymer oligonucleotides (dA₁₅, dG₁₅, dC₁₅, and dT₁₅). The dispersed nanotube concentration and degree of exfoliation were measured for each nucleobase. The nanotubes were more highly exfoliated and more temporally stable in dC₁₅ and dT₁₅. While the degree of exfoliation was relatively time independent, absorption and photoluminescence spectra showed definite changes over time after the initial sample preparation. In particular, photoluminescence signals appeared at well-defined times, consistent with previous evidence of time-dependent DNA wrapping followed by oxide removal. Analysis of the nanotubes’ optical properties, including circular dichroism, suggests that all bases except adenine stack onto the nanotube surface. In contrast, dA₁₅ is unstable on the nanotube surface and eventually returns to a self-stacked arrangement. The order of the dispersion efficiencies was found to be T > C > G ≫ A, where thymine produced the most intense NT optical signals and cytosine was seen to wrap SWNTs the fastest.