16 May 2011
from NatureAsia Website


Molecules of single-stranded DNA can be moved into and out of carbon nanotubes using electric fields.




A transmission electron microscopy image (top) and simulations (lower panels)

showing the encapsulation of a DNA molecule in a double-walled carbon nanotube



Carbon nanotubes are attracting significant interest for biological and biomedical applications due their low cell toxicity and unique ability to easily penetrate cell membranes.


These characteristics make carbon nanotubes potentially ideal vectors for the delivery of biomolecules into living cells. The single-walled nanotubes (SWNTs) typically examined for such applications, however, are too narrow to accommodate a useful payload.


Double-walled carbon nanotubes (DWNTs), on the other hand, have a much larger internal diameter and could be loaded with a range of complex molecules. DWNTs are also more mechanically sound and thermally stable compared with SWNTs.

Yongfeng Li and co-workers from Tohoku University in Japan and the Shanghai Institute of Applied Physics in China have now developed a method for loading DWNTs with single-stranded DNA and releasing it under controlled conditions.1


The team was able to move the DNA molecules into and out of DWNTs using an electric field by changing the field’s polarity.

The researchers used 30 base-long cytosine homopolymers as the DNA molecule. Under a positive electric field, the DNA was induced to enter the 4 nm-wide cavity of the DWNTs in aqueous solution (see image), where it formed a coil-like structure. Simply applying a negative electric field then triggered the DNA molecule to be ejected from the DWNT back into solution.

This system shows considerable promise for the encapsulation and release of DNA, but the researchers found that the process becomes increasingly difficult to induce as the number of bases increases.


The team suggests that this resistance to encapsulation may be due to strong electron stacking interactions between the DNA and the DWNTs - a resistance that could possibly be overcome by applying a radiofrequency voltage signal in addition to the direct current power source to stretch and orient the DNA molecules in a way that facilitates encapsulation.

Li and his co-workers are already planning the next steps of their encapsulation research.

“We plan to make conjugates of DNA and gold nanoparticles, which will be encapsulated into carbon nanotubes and manipulated by laser irradiation of the gold nanoparticle,” says Li.


“We expect the force generated by light pressure to drive the DNA out of carbon nanotubes.”




  1. Li, Y.1, Chen, S.2, Kaneko, T.1 & Hatakeyama, R.1 Electrically moving single-stranded DNA into and out of double-walled carbon nanotubes. Chem. Commun. 47, 2309–2311 (2011). | article


Author affiliation

  1. Department of Electronic Engineering, Tohoku University, Sendai 980-8579, Japan

  2. Shanghai Institute of Applied Physics, Chinese Academic of Science, Shanghai, 201800, China