Why ssDNA chains with different sequences selectively adsorb on carbon nanotubes (CNTs) of different properties has puzzled experimental and theoretical scientists for over a decade. In our work, we focus on physical aspects of the problem using a coarse-grained model for the ssDNA-CNT system. Our Monte Carlo simulations reveal significant differences in the adsorbed conformations and adsorption thermodynamics of three investigated sequences of guanine (G) and thymine (T): G12, T12, and (GT)6. The competition between base-base and base-nanotube interactions results in ordered but distinct equilibrium adsorbed conformations in the case of the homopolymer chains, and more disordered conformations for the heteropolymer. More generally, the larger guanine bases show preference to be stacked against the nanotube, while the smaller thymine bases remain stacked with neighboring bases. This frustration leads to the disordered conformations observed in the case of (GT)6. It is shown that this competition also leads to greater sensitivity of this sequence towards nanotubes of different diameter compared with the homopolymeric sequences. Our findings confirm and elucidate why heteropolymers are used for selective adsorption of CNTs in experimentation.
simchas@technion.ac.il
