Modifying the electronic properties of single-walled carbon nanotubes using designed surfactant peptides

• Published in: Nanoscale Vol. 4; no. 15; pp. 4544 - 4554
• Main Authors: Samarajeewa, Dinushi R, Dieckmann, Gregg R, Nielsen, Steven O, Musselman, Inga H
• Format: Journal Article
• Language: English
• Published: England 07.08.2012
• Subjects: Amino Acid Sequence; Circular Dichroism; Electronics; Microscopy, Atomic Force; Nanotubes, Carbon - chemistry; Peptides - chemical synthesis; Peptides - chemistry; Protein Structure, Secondary; Spectroscopy, Near-Infrared; Surface-Active Agents - chemistry
• ISSN: 2040-3364; 2040-3372
• DOI: 10.1039/c2nr30423f

The electronic properties of carbon nanotubes can be altered significantly by modifying the nanotube surface. In this study, single-walled carbon nanotubes (SWCNTs) were functionalized noncovalently using designed surfactant peptides, and the resultant SWCNT electronic properties were investigated. These peptides have a common amino acid sequence of X(Valine)(5)(Lysine)(2), where X indicates an aromatic amino acid containing either an electron-donating or electron-withdrawing functional group (i.e. p-amino-phenylalanine or p-cyano-phenylalanine). Circular dichroism spectra showed that the surfactant peptides primarily have random coil structures in an aqueous medium, both alone and in the presence of SWCNTs, simplifying analysis of the peptide/SWCNT interaction. The ability of the surfactant peptides to disperse individual SWCNTs in solution was verified using atomic force microscopy and ultraviolet-visible-near-infrared spectroscopy. The electronic properties of the surfactant peptide/SWCNT composites were examined using the observed nanotube Raman tangential band shifts and the observed additional features near the Fermi level in the scanning tunneling spectroscopy dI/dV spectra. The results revealed that SWCNTs functionalized with surfactant peptides containing electron-donor or electron-acceptor functional groups showed n-doped or p-doped altered electronic properties, respectively. This work unveils a facile and versatile approach to modify the intrinsic electronic properties of SWCNTs using a simple peptide structure, which is easily adaptable to obtain peptide/SWCNT composites for the design of tunable nanoscale electronic devices.