Selective Suspension of Single-Walled Carbon Nanotubes Using β‑Sheet Polypeptides

Individual single-walled carbon nanotubes (SWNTs) were suspended in water using amphipathic β-sheet peptides of the general sequence Ac-(XKXE)₂-NH₂. By substituting natural and nonnatural amino acids of varying aromatic and hydrophobic character in the X position, the interactions between the peptide and the nanotube sidewall could be systematically varied. Surprisingly, enhancing the degree of favorable π–π and hydrophobic interactions, which strongly influence the self-assembly properties of these peptides, did not correlate with an improvement in nanotube dispersion efficiency. We found that substituents in the X-position of the peptides play a significant role in SWNT interaction and contributes to (<i>n</i>,<i>m</i>) structure specificity

Bright Fraction of Single-Walled Carbon Nanotubes through Correlated Fluorescence and Topography Measurements

Correlated measurements of fluorescence and topography were performed for individual single-walled carbon nanotubes (SWNTs) on quartz using epifluorescence confocal microscopy and atomic force microscopy (AFM). Surprisingly, only ∼11% of all SWNTs in DNA-wrapped samples were found to be highly emissive on quartz, suggesting that the ensemble fluorescence quantum yield is low because only a small population of SWNTs fluoresces strongly. Qualitatively similar conclusions were obtained from control studies using a sodium cholate surfactant system. To accommodate AFM measurements, excess surfactant was removed from the substrate. Though individual SWNTs on nonrinsed and rinsed surfaces displayed differences in fluorescence intensities and line widths, arising from the influence of the local environment on individual SWNT optical measurements, photoluminescence data from both samples displayed consistent trends