(Invited) Spectroscopic Titration Shows (n,m)-Dependent Displacement of SDS By ssDNA on Single-Wall Carbon Nanotubes

Abstract

Single-stranded DNA oligonucleotides (ssDNA) are uniquely customizable polymers that are useful for coating, suspending, and structurally sorting single-wall carbon nanotubes (SWCNTs) in water. However, SWCNT dispersions are instead commonly prepared using inexpensive amphiphilic surfactants such as SDS. By monitoring changes in the nanotube fluorescence wavelengths and intensities, we show that such SDS coatings on dispersed SWCNTs can be controllably displaced by the addition of small amounts of ssDNA. The displacement data can be well represented by kinetic modeling, giving the time scales for equilibration of the coating composition. We measured spectra of SWCNT samples that were dispersed in low concentrations of SDS, then treated with small amounts of ssDNA, and allowed to reach equilibrium. Plots of the final spectral shifts as a function of added ssDNA provide (n,m)-specific “titration” curves that show strongly diameter-dependent behavior. Smaller diameter nanotubes undergo SDS displacement at the lowest ssDNA concentrations. The limiting spectral shifts suggest that SWCNT surfaces become coated with adsorbed SDS as well as ssDNA. We will illustrate how the (n,m)-dependent displacements found here can be used for structural sorting of mixed SWCNT samples.