Scanning Tunneling Spectroscopy Reveals Electronic Structure of DNA Molecules

In a recent publication, researchers in the field of molecular biophysics have presented the electronic structure of single DNA molecules.

Investigators at the Hebrew University of Jerusalem (Israel) and the University of Modena e Reggio Emilia (Italy) and other collaborators used a combination of advanced instrumentation and quantum theory to produce the findings that were published in the January 2008 issue of the journal Nature Materials.

The technique called scanning tunneling spectroscopy (an off-shoot of scanning tunneling microscopy, or STM) had been used for nearly 20 years to resolve the energy-level structure of single DNA molecules without success. STM is a powerful way to view surfaces at the atomic level by probing the density of states of a material using tunneling current. For STM, good resolution is considered to be 0.1 nm lateral resolution and 0.01 nm depth resolution. STM can be used not only in ultra high vacuum but also in air and various other liquid or gas ambients, and at temperatures ranging from near zero Kelvin to a few hundred degrees Celsius.

The STM method is based on the concept of quantum tunneling. When a conducting tip is brought very near to a metallic or semiconducting surface, a bias between the two can allow electrons to tunnel through the vacuum between them. Variations in current as the probe passes over the surface are translated into an image. STM is a challenging technique, as it requires extremely clean surfaces and sharp tips.

In the current study, the investigators worked at minus 195 degrees Celsius to measure the current that passed across a poly(G)–poly(C) DNA molecule deposited on a gold substrate. Quantum equations applied to the images that were obtained allowed identification of the parts of the double helix that contribute to the charge flow along the molecule.

These findings are expected to be of importance to researchers in many scientific areas from biochemistry to nanotechnology. They are especially relevant to the field of nano-bioelectronics, where DNA is being used to form conducting molecular wires in molecular computing networks that are smaller and more efficient than those produced today with silicon technology.


Related Links:
Hebrew University of Jerusalem
University of Modena e Reggio Emilia