Optical identification of a DNA-wrapped carbon nanotube: Signs of helically broken symmetry

Optical absorption spectra and circular dichroism for DNA-wrapped single-walled carbon nanotube (SWNT) was investigated. The DNA-SWNT hybrid structure was simulated by the help of NAMD package with CHARMM parameterization. The chiral perturbation of the DNA lifts selection rules and allows additional optical transitions in the DNA-SWNT hybrid that were prohibited by symmetry in the bare nanotube for cross-polarized absorption. The optical circular dichroism spectra for a variety of SWNT-DNA hybrids show strong dichroism for originally achiral as well as chiral tubes. The hybrid material is predicted to show splitting and a shift of the lowest peak when, with sufficient wrapping coverage. The optical activity must be fully attributed to the nanotube itself and to its helical symmetry breaking.