DEFECTS AND CONDUCTIVITY OF DNAS

Conductor or insulator? The debate about the conductivity of DNA have been recently revived due to contradictory results of transport measurements on a small number of molecules deposited on a substrate and connected to metallic electrodes, and an answer to this question is important for DNA based molecular electronics. In several works it was observed that double-stranded DNA molecules are conducing (semicoducting, metallic or even superconducting due to proximity induced superconductivity) [1-3]. However in other works DNA was found to be insulating [4], even when the molecules had perfectly ordered base pairs. In this report we argue the conductivity of DNAs dependes on defects in the molecules. At first we consider the global defect of the DNAs structure due to the interaction of the molecules with the underlying substrate. For most commonly used substrates like mica or silicon oxide the interaction between the molecule and the surface is very strong and induces a very large compression deformation of deposited DNAs. The thickness of such compressed DNAs is 2–4 times less than the diameter (about 2 nm) of native Watson-Crick B-DNA [4]. Here we confir