Understanding the Electrophoretic Separation of Single-Walled Carbon Nanotubes Assisted by Thionine as a Probe

Single-walled carbon nanotubes (SWNTs) dispersed by sodium dodecyl sulfate (SDS) can be simply and effectively separated into semiconducting (s) and metallic (m) fractions by the method of agarose gel electrophoresis, in which s-SWNTs cannot migrate like m-SWNTs and remain unmoved under electric field. The role of SDS is suggested to be crucial for such separation effect. Its mechanism, however, is still unclear and hard to probe. In the present study, by employing thionine (TN), a positively charged dye molecule which may show unique interaction with SDS molecules, we can roughly evaluate the changes of SDS aggregates during the agarose gel electrophoresis. On the basis of the results of the electrophoretic and spectroscopic characterizations, we propose that the unique interaction of s-SWNTs with agarose and the exfoliation of some SDS molecules from SDS-s-SWNT entities lead to the separation of s- and m-SWNTs.