Electrostatic trapping technique has been used to insert a few DNA molecules into the gap between two Pt electrodes as is illustrated in the picture. Thus it was possible to test the electrical properties of DNA. The measurements suggest that the DNA conductance is similar to that of a large band gap semiconductor. In the experiment, the electrodes were separated by just about 8 nm. The 10-nm-long DNA double-helix links the electrodes and provides a path for the electrical current. It was suggested that the DNA conductance is due to the fact that each electron assumes a wavefunctions that is a superposition of many localized states, called orbitals. Although each orbital belongs to some particular base of the DNA, each electron has no definite position and can by visualized as a cloud spread over the entire DNA molecule. Since the molecule is not too long in these experiments, electrons can assume such sates that have a position uncertainty at least as large as the length of the DNA. By the Heisenberg Uncertainty Principle, such electrons can have a quite definite momentum and thus contribute significantly to the net electrical current flowing along the molecules. This explains why the DNA molecule can have a nonzero electrical conductance.
1. D. Porath, A. Bezryadin, S. de Vries, and C. Dekker, "Direct measurements of electrical transport through DNA molecules," Nature 403, 635–638, 2000.
|
