The Study of Charge Transport in Nanoscale DNA Structures
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The Study of Charge Transport in Nanoscale DNA Structures G. Bart, M. R. Singh and M. Zinke-Allamang Department of Physics and Astronomy, University of Western Ontario, London, Canada N6G 3K7 ABSTRACT We have studied the variable range hopping (VRH) mechanism for polarons in DNA structures using an exponential density of states. Due to the electron-phonon interaction localized polarons are formed in the DNA helix. The unwinding of DNA increases molecular orbital overlap between bases while decreasing the base-to-base distance. These types of vibrations create phonons. We consider that DNA has a band tail which has an exponential density of states and we have calculated the temperature- and the electric field dependence of the conductivity. We compare our model with the experiments of the electrical conductivity of samples of double-stranded H5N1 genes of avian Influenza virus DNA. Our theory is able to explain their data. Keywords: DNA, Conductivity, Hopping, Localization, Nanotechnology
Introduction DNA molecules and their derivatives, such as deoxyguanosine are attracting attention for the fabrication of nano-devices. Their attractive feature for nano-science is their self-assembling capability, which can be used in nano-electronics, molecular computing, and biosensors [1]. The aim of the present paper is to study the charge conductivity of DNA structures at high temperature and high electric field. Direct measurements of conduction in DNA were performed by Fink and Schönenberger [2]. Their results illustrate the current-voltage relationship of ropes composed of λ-bacteriophage DNA with lengths on the order of a few hundred nanometers. They found a nearly linear relationship between applied voltage and observed current at low voltage but were unable to determine the precise mechanism for the charge transport. More recently, there have been a number of experiments which indicate more precisely the nature of the charge transport mechanism in DNA. One such study by Porath et al. [3] indicates that there is large band gap semiconducting behavior. Another experiment on λ-bacteriophage DNA by Tran et al. [4] measures its conductivity across a range of temperatures through the use of an optical cavity operating at 12GHz and 100GHz. They found that the conductivity of their samples became strongly temperature dependent. Experiments performed by Yoo et al. [5] measured the electric field dependence of the current through samples of poly(dG)-poly(dC) and poly(dA)-poly(dT) DNA. Their results demonstrate the temperature dependence of the conductivity of DNA as well as its non-linear current-voltage relationship. They suggested that charge conduction is due to the hopping mechanism. Experiments have also been conducted with influenza DNA molecules suspended between two single-walled carbon nanotubes attached to gold electrodes [6]. Both single- and doublestranded DNA molecules were tested in a vacuum and in ambient conditions. A non-linear increase in current with voltage was observed. Carbon nanotubes, with their chemical, e
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