Recognition ability of DNA for carbon nanotubes correlates with their binding affinity.

The ability to sort mixtures of carbon nanotubes (CNTs) based on chirality has recently been demonstrated using special short DNA sequences that recognize certain matching CNTs of specific chirality. In this work, we report on a study of the relationship between recognition sequences and the strength of their binding to the recognized CNT. We have chosen the (6,5) CNT and its corresponding DNA recognition sequences for investigation in this study. Binding strength is quantified by studying the kinetics of DNA replacement by a surfactant, which is monitored by following shifts in the absorption spectrum. We find that recognition ability correlates strongly with binding strength thus measured; addition or subtraction of just one base from the recognition sequence can enhance the kinetics of DNA displacement some 20-fold. The surfactant displaces DNA in two steps: a rapid first stage lasting less than a few seconds, followed by progressive removal lasting tens of minutes. The kinetics of the second stage is analyzed to extract activation energies. Fluorescence studies support the finding that the DNA sequence that recognizes the (6,5)-CNT forms a more stable hybrid than its close relatives.