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 (dA(15), dG(15), dC(15), and dT(15)). The dispersed nanotube concentration and degree of exfoliation were measured for each nucleobase. The nanotubes were more highly exfoliated and more temporally stable in dC(15) and dT(15). 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, dA(15) 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.