Optimizing the Purification of Biofunctionalized Carbon Nanotubes

The utilization of single-walled carbon nanotubes (SWNTs) in large quantities for molecular electronics, optoelectronics, biosensors, and medical applications will require SWNTs of the same physical structure, electronic type, and band gap. Since current methods of synthesis produce mixtures of nanotubes with different physical structures and electrical properties, the development of strategies for the postproduction separation of these one-dimensional materials is highly desirable. In this work, we demonstrate a scalable method for separating SWNTs by diameter using density gradient centrifugation. Of particular interest for biosensing applications is the bulk purification of SWNTs through centrifugation of DNA wrapped SWNTs in aqueous density gradients. The dependence of this process on DNA sequence and length has been determined. In addition, strategies for decreasing the purification time are outlined. Overall, this nondestructive and scalable separation strategy is expected to impact a variety of applications for SWNTs where monodisperse structure and properties are essential.