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Nanoscale Research Letters

, 12:316

First Online: 27 April 2017Received: 23 December 2016Accepted: 13 April 2017DOI: 10.1186-s11671-017-2076-y

Cite this article as: Abdalla, S., Obaid, A. & Al-Marzouki, F.M. Nanoscale Res Lett 2017 12: 316. doi:10.1186-s11671-017-2076-y


BackgroundDeoxyribonucleic acid DNA is one of the best candidate materials for various device applications such as in electrodes for rechargeable batteries, biosensors, molecular electronics, medical- and biomedical-applications etc. Hence, it is worthwhile to examine the mechanism of charge transport in the DNA molecule, however, still a question without a clear answer is DNA a molecular conducting material wire, semiconductor, or insulator? The answer, after the published data, is still ambiguous without any confirmed and clear scientific answer. DNA is found to be always surrounded with different electric charges, ions, and dipoles. These surrounding charges and electric barriers due to metallic electrodes as environmental factors EFs play a substantial role when measuring the electrical conductivity through λ-double helix DNA molecule suspended between metallic electrodes. We found that strong frequency dependence of AC-complex conductivity comes from the electrical conduction of EFs. This leads to superimposing serious incorrect experimental data to measured ones.

MethodsAt 1 MHz, we carried out a first control experiment on electrical conductivity with and without the presence of DNA molecule. If there are possible electrical conduction due to stray ions and contribution of substrate, we will detected them. This control experiment revealed that there is an important role played by the environmental-charges around DNA molecule and any experiment should consider this role.

Results and discussionWe have succeeded to measure both electrical conductivity due to EFs σENV and electrical conductivity due to DNA molecule σDNA independently by carrying the measurements at different DNA-lengths and subtracting the data. We carried out measurements as a function of frequency f and temperature T in the ranges 0.1 Hz < f < 1 MHz and 288 K < T < 343 K. The measured conductivity σMES portrays a metal-like behavior at high frequencies near 1 MHz. However, we found that σDNA was far from this behavior because the conduction due to EFs superimposes σDNA, in particular at low frequencies. By measuring the electrical conductivity at different lengths: 40, 60, 80, and 100 nm, we have succeeded not only to separate the electrical conduction of the DNA molecule from all EFs effects that surround the molecule, but also to present accurate values of σDNA and the dielectric constant of the molecule ε’DNA as a function of temperature and frequency. Furthermore, in order to explain these data, we present a model describing the electrical conduction through DNA molecule: DNA is a classical semiconductor with charges, dipoles and ions that result in creation of localized energy-states LESs in the extended bands and in the energy gap of the DNA molecule.

ConclusionsThis model explains clearly the mechanism of charge transfer mechanism in the DNA, and it sheds light on why the charge transfer through the DNA can lead to insulating, semiconducting, or metallic behavior on the same time. The model considers charges on DNA, in the extended bands, either could be free to move under electric field or localized in potential wells-hills. Localization of charges in DNA is an intrinsic structural-property of this solitaire molecule. At all temperatures, the expected increase in thermal-induced charge is attributed to the delocalization of holes or-and electrons in potential hills or-and potential wells which accurately accounts for the total electric and dielectric behavior through DNA molecule. We succeeded to fit the experimental data to the proposed model with reasonable magnitudes of potential hills-wells that are in the energy range from 0.068 eV.

KeywordsAC-complex conductivity DNA molecule Environmental and surrounding charges Localized charges Potential hills-wells Dielectric constant AbbreviationsC∞Measured capacitance at very high frequencies

CBConduction band

CdcMeasured capacitance at very low frequencies

CTCharge transfer

DNADeoxyribonucleic acid


ECEnergy state of the conduction band

EC0Most probable value in the conduction band within the Gaussian distribution

EFsEnvironmental factors

EgForbidden gap

EVEnergy state of the valence band

EV0Most probable value in the valence band within the Gaussian distribution


gGaussian-integral limits

G∞Measured capacitance at very high frequencies

GdcMeasured conductance at very low frequencies

gγDepth of the potential well

HTrapping hole-level H1, H2, H3, H4, H5

HOMOHighest occupied molecular orbital

idriftDrift current through a diode

igenGeneration current through a diode

isatSaturation current through a diode

LLength of molecule

LESsLocalized energy-states

LUMOLowest unoccupied molecular orbital

PECGaussian probability to find certain localized energy state within the conduction band

PEVGaussian probability to find certain localized energy state within the valiancy band

RDNACDNAParallel electronic circuit represents the electrical effect of charges through DNA molecule

REVNCENVParallel electronic circuit represents the electrical effect of the environmental charges, ions, and dipoles


uReduced energy u = gγ-kT

VBValence band

αConstant of dimensions nm.eV

ε’DNADielectric constant due to DNA

ϕPotential barrier, eV

γDisorder energy

σDNAElectrical conductivity due to DNA

σENVElectrical conductivity due to EFs

σMESMeasured conductivity

τRelaxation time of electric charges

τ0Relaxtion time of charge without disorder without localization

Autor: S. Abdalla - A. Obaid - F. M. Al-Marzouki

Fuente: https://link.springer.com/

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