Atomic Force Microscopy Studies of DNA-Wrapped Carbon Nanotube Structure and Binding to Quantum Dots

TLDR

Single‑stranded DNA noncovalently disperses individual single‑walled carbon nanotubes, creating a CNT–DNA hybrid that facilitates separations and diverse applications. The authors wrapped CNTs with thiol‑modified DNA to form stable CNT–DNA/CdSe/ZnS quantum‑dot conjugates, and AFM imaging revealed the DNA’s location on the nanomaterial. AFM showed a regular, DNA‑dependent pattern—helical turns of ~14‑nm pitch arranged end‑to‑end in a single layer—distinct from SDS‑dispersed CNTs, confirming that quantum‑dot functionalization covers the CNT surface without damaging it.

Abstract

Single-stranded DNA is an effective noncovalent dispersant for individual single-walled carbon nanotubes (CNTs) in aqueous solution, forming a CNT−DNA hybrid material that has advantages for CNT separations and applications. Atomic force microscopy (AFM) reveals a regular pattern on the surface of CNT−DNA. We found this pattern to be independent of the length and sequence of the wrapping DNA, yet different from the structures observed for CNTs dispersed with sodium dodecyl sulfate in the absence of DNA. We wrapped CNTs with thiol-modified DNA to form stable conjugates of CNT−DNA and core/shell CdSe/ZnS quantum dots; AFM imaging of these conjugates identified for the first time the location of DNA on the CNT−DNA nanomaterial. Our results suggest that the AFM pattern of CNT−DNA is formed by helical turns (∼14-nm pitch) of wrapped DNA strands that are closely arranged end-to-end in a single layer along the CNT. This work demonstrates the useful functionalization of CNTs with quantum dots in a manner that avoids direct, destructive modification of the CNT surface and suggests nearly complete surface coverage of the nanotubes with DNA.