Authors: S.E. Snyder, S.V. Rotkin
Affilation: Lehigh University, United States
Pages: 27 - 30
Keywords: carbon nanotubes, optical absorption, DNA, circular dichroism
Single-walled carbon nanotubes (SWNTs) hold great promise for the next generation of electronic devices due to their small, biologically compatible size, exceptional electronic properties, and the range of bandgaps accessible with variations in diameter and symmetry. Large scale fabrication of nanotube-based devices requires a robust dispersion method that must overcome nanotube insolubility and strong van der Waals attraction between tubes. Noncovalent functionalization of SWNTs with helically wrapped single-stranded DNA yields stable hybrid structures that disperse in aqueous solution. Envisioning optoelectronic applications of nanotubes, we investigate whether the optical properties of DNA-wrapped SWNTs are different than those of bare nanotubes. Our earlier work showed that the direct optical bandgap decreases with the presence of DNA wrapping. This is consistent with experiments using standard geometry in which incident light is polarized along the nanotube axis . Here we consider optical absorption with perpendicular (or circular) polarization, which has been measured for SWNTs dispersed using a surfactant. We find changes in absorption spectra upon hybridization with DNA, including new transitions prohibited for pristine nanotubes in the same polarization. In addition, we find circular dichroism for non-chiral SWNTs. These optical effects are predicted to serve as qualitative tools to directly identify the DNA wrapping.