Journal of the Korean Physical Society, Vol. 50, No. 3, March 2007, pp. 902∼904
Transport Study of Lambda DNA Molecules
J. S. Hwang, M. H. Son, J. H. Oh and D. Ahn∗
Institute of Quantum Information Processing and Systems, University of Seoul, Seoul 130-743
S. H. Hong, H. K. Kim and S. W. Hwang†
Department of Electronics and Computer Engineering, Korea University, Seoul 136-075 and
Institute of Quantum Information Processing and Systems, University of Seoul, Seoul 130-743
(Received 3 September 2006, in final form 26 December 2006)
We fabricated lambda DNA nanowire interconnections between nanometer-scale electrodes and
measured their electrical transport characteristics. By spraying a diluted solution of lambda
DNA molecules, DNA interconnections were formed between parallel Ti/Au electrodes with a
gap of 1 µm. These lambda DNA nanowires showed good electrical transport characteristics.
The current-voltage characteristics exhibited conductance values ranging from 0.21 to 0.65 nG,
which are consistent with previous reports. The results in this experiment provide evidence for
the conducting properties of DNA molecules and provide possibilities of using DNA molecules as
interconnecting materials in bio-nano electronic systems.
PACS numbers: 73.63.-b, 87.14.Gg
Keywords: Lambda DNA, Nanowire, Molecule, Transport, Electrical conduction
ies on electrical transport through DNA molecules.
Watanabe et al. [4] measured the charge transfer in
salmon sperm DNA by using an electric triple probe.
Fink and Schönenberger [7] measured a linear metallic current-voltage (I-V) characteristic from micrometerscale lambda DNA ropes. Porath et al. [8] and Hwang
et al. [9] observed semiconducting I-V characteristics
with clear voltage gaps from poly(dG)-poly(dC) DNA
molecules. On the other hand, Braun et al. [10] measured no observable current from lambda DNA on mica
substrates. Storm et al. [11] also observed insulating
properties for DNA molecules greater than 40 nm in
length. Consequently, the electrical transport property
of DNA molecules has not yet been clearly explained.
In this paper, we report our experimental results
for the electrical transport characteristics of lambda
DNA molecules. We measured the I-V characteristics
to demonstrate the electrical conducting behavior of
lambda DNA molecules.
I. INTRODUCTION
Electrical transport through molecules is important
due to interesting new physics and possible applications
to future electronic devices [1–6]. The major advantage
of molecules is their small sizes, and we can expect various interesting properties to originate at the molecular level. Molecular materials include deoxyribonucleic
acids (DNAs), nanowires, quantum dots, organic polymers, and others. Among them, DNA has many unique
functional and structural advantages [2–5]. The diameter of the synthesized DNA double helix structure is 2
nm, and the length can be controlled by the number of
base pairs in a unit of 0.34 nm, while suggests that DNA
is a length controllable nanowire and could be used as
electrical wiring in nano devices. While electron-beam
lithography or other nano fabrication techniques are capable of producing metal wires with controlled widths
below 10 nm, the fabrication process is very complex,
and the productivity is very low. Therefore, DNA may
be applied as a nanowire interconnection for nanometerscale electronic device engineering [4–6].
Examination of the electrical conduction properties
of DNA molecules is essential for electronic device applications. Until now, there have been many stud∗ E-mail:
† E-mail:
II. EXPERIMENTAL PROCEDURES
The specimens used in this experiment were commercial lambda DNA molecules purchased from Promega
Corporation [12]. The length of the lambda DNA was
approximately 16.5 µm, equivalent to 48502 base pairs.
The DNA molecules were provided in a buffer solution
[email protected];
[email protected]
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Transport Study of Lambda DNA Molecules – J. S. Hwang et al.
Fig. 1. AFM image of lambda DNA nanowires connecting
the electrodes. The scan area is 10 µm × 10 µm, and the
four arrows indicate the DNA nanowires.
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Fig. 2. Room temperature I-V characteristics of three different lambda DNA nanowires (DNAs between the electrodes
1-2, 2-3, and 3-4 shown in Fig. 1).
less than 1 pA.
consisting of 10-mM Tris-HCl (pH 7.8), 10-mM NaCl,
and 1-mM EDTA (ethylenediamine tetraacetic acid).
The concentration of the as-delivered lambda DNA solution was more than 400 µg/ml, and it was diluted with
deionized water to a concentration of 10 ng/µl. The quality of the deionized water and the concentration of the
buffer solution were carefully controlled to preserve the
homogenous distribution of the DNA molecules in the
solution.
Nanometer-scale electrode patterns were fabricated by
using standard electron-beam lithography and liftoff.
The substrate was a p-type silicon wafer, and 200-nmthick SiO2 was deposited as an insulating layer. Twelve
(12) parallel metal electrodes were made by electron
beam evaporation of a Ti adhesion layer with a thickness of 5 nm, followed by an Au conducting layer with a
thickness of 10 nm. The width of the electrode pattern
was 500 nm, and the spacing between the electrodes was
1 µm.
An acid piranha solution (H2 SO4 : H2 O2 = 3 : 1) was
used to make the SiO2 surface hydrophilic and, thus,
enhance the adhesion of lambda DNA to the surface. A
1-µl drop of lambda DNA solution was applied to the Au
electrodes by using a micropipette. The nitrogen blow
dry in a direction perpendicular to the electrodes was
done after waiting for about 1 min. This blowing process
helps DNA nanowires align between the electrodes.
Atomic force microscopy (AFM) was employed to examine images of lambda DNA nanowires between the
metal electrodes. AFM measurements were done by using a PSIA XE-100 microscope in the non-contact mode
(known as the tapping mode). Transport measurements
were performed in air and at room temperature by using
a voltage source (Keithley 230) and a precision preamplifier (DL instruments 1211). The system noise level was
III. DATA AND DISCUSSION
Fig. 1 shows an AFM image of lambda DNA nanowires
between the electrodes. The AFM scan area is 10 µm
× 10 µm, and the shape and the dimension of the
metal electrodes can be identified from the AFM image. Lambda DNA nanowires between the metal electrodes are clearly observed as marked by the four arrows
in Fig. 1. Two lambda DNA molecules are connecting
electrodes 1 and 2. On the other hand, one lambda
DNA molecule is connecting electrodes 2 and 3. Another
lambda DNA molecule is identified in between electrodes
3 and 4.
The width and the height of these four lambda DNA
molecules in Fig. 1 are around 30 nm and 2 nm, respectively, from the AFM image analysis. Double-stranded
lambda DNA has a diameter of 2 nm, thus, the lambda
DNA nanowires in our experiments are in the shape of
bundles.
The bundle formation of DNA is easily induced by
adding a monovalent cationic surfactant to the solution
[13] or by changing the concentration of the DNA solution [14]. In our case, the change in the concentration
during the dilution process causes bundle formation. The
lambda DNA bundle in Fig. 1 consists of more than 10
double-stranded lambda DNA molecules.
Fig. 2 shows room-temperature I-V characteristics measured from the three different lambda DNA
nanowires (the DNA nanowires between electrodes 1-2,
2-3, and 3-4) shown in Fig. 1. All the measurements from
these electrode pairs show almost a monotonic increase
in the current with increasing bias in the range from –1 to
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Journal of the Korean Physical Society, Vol. 50, No. 3, March 2007
1 V. However, the conductance (slope) of the three samples varies. To estimate the differences, we obtained the
zero-field conductances of the three different samples by
differentiating the I-V curve at zero bias. The obtained
values are 0.65, 0.31, and 0.21 nG for electrodes 1-2, 2-3,
and 3-4, respectively. The conductance of lambda DNA
between electrodes 1-2 is almost two times larger than
the values from the conductance for electrodes 2-3 and
3-4. Two DNA nanowires are connected between electrodes 1-2 and one is connected between electrode 2-3
and 3-4. Our measured conductance values are commensurate with the number of DNA molecules.
Only a few studies were reported for conductance
measurements of lambda DNA nanowires. Fink and
Schönenberger reported a 2.5-MΩ resistance value from
600-nm-long lambda DNA ropes [7]. Inomatai et al.
found that the electrical resistance of lambda DNA
molecules between fine electrodes had a large variation
from 7.8 MΩ to the values larger than 1 TΩ [15]. Considering the large variations in dimension, geometry, contact
material and others, the conductance values in our experiment are within a similar range as those in previous
reports.
In Fig. 2, nonlinear I-V characteristics are observed
from the DNA nanowire in between electrodes 1-2, which
might originate from an asymmetric contact potential
between the contact metal and the DNA molecules. The
contact mechanism between metals and DNA molecules
is intriguing, and it has not yet been clearly explained.
The electrical transport study in this experiment demonstrates a direct electrical measurement of lambda DNA
nanowires, and we obtain good electrical conducting
properties from this molecular system.
IV. CONCLUSION
We fabricated lambda DNA nanowire interconnections between nanometer-scale electrodes and measured
their electrical transport characteristics. Lambda DNA
nanowires were successfully connected between the electrodes and showed good electrical transport characteristics. The I-V measurements showed that the conductance values ranged from 0.21 to 0.65 nG, which is consistent with previous reports. The results in this experiment provide evidence for the conducting properties of DNA molecules and possibilities for using DNA
molecules as interconnecting materials in various bionano systems.
ACKNOWLEDGMENTS
This work was supported by the Creative Research
Initiatives program of Ministry of Science and Technology/Korea Science and Engineering Foundation under
contract No. R16-1998-009-01001-0(2006) and by the
Brain Korea 21 project in 2006.
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