Carbon Nanotube—Biomolecule Interactions: Applications in Carbon Nanotube Separation and Biosensing

We describe a DNA-carbon nanotube hybrid material that has proven useful for dispersion and structure-based separation. Single-stranded DNA binds strongly to carbon nanotubes, rendering them dispersable in water as charged colloidal particles. These can be subjected to separation techniques. Certain sequences form hybrids that allow separation on the basis of the properties of the core nanotube material. Carbon nanotubes dispersed by a non-ionic surfactant can also be separated by an alternative technique. Molecular models suggest that the hybrid structure consists of helical wrapping of the DNA around the nanotube, in good agreement with AFM data. We propose that the separation mechanism relies on modulation of the electric field of the DNA phosphate charge by interactions with the nanotube core. Finally, we show an example of the use of carbon nanotube-biomolecule interactions for detection using a CNT-based field effect transistor.