makes DNA more conductive
Technology Research News
For several years, scientists have explored
ways to make DNA conduct electricity. DNA’s size and ability to arrange
itself, or self-assemble, would make conductive DNA a valuable material
for nanoscale circuitry.
One group of researchers has replaced parts of DNA’s base pairs with metal
ions in order to allow electrons to flow through the molecule.
Biological DNA, found in the nucleus of every cell, is essentially composed
of long strands of four bases -- adenine, guanine, cytosine, and thymine.
The researchers engineered the conductive DNA by coaxing the base pairs
to exchange a proton for a zinc ion. The addition of metal made DNA behave
like a semiconductor.
“The substitution of the imino proton with a zinc ion makes the DNA hundreds
of times more conductive,” said researcher Jimmy Xu, an engineering and
physics professor at Brown University.
The engineered DNA could eventually be used in microelectronics where
there is a need for tiny, self-assembling conductors. The DNA could be
the basis for “a new material system that can be controllably produced,
whose properties can be…engineered, and whose ensemble can self-organize
into functional structures and can collectively process massive amount
of information,” said Xu.
“DNA is the basic and best understood building block -- a perfect place
to start engineering,” he said.
Engineering DNA molecules to accept the zinc was relatively simple, according
to Xu. Previous research by team member Jeremy Lee, a biochemistry professor
at the University of Saskatchewan, had already established that DNA readily
absorbs ions of zinc, nickel and cobalt at high pH levels.
Xu’s team raised the DNA’s pH level to 9.0 by adding zinc ions containing
acids to a test tube of DNA. The DNA molecules released the imino protons
in their base pairs and took up zinc ions instead, resulting in a modified,
metallic compound DNA , or M-DNA.
The conductivity of any substance depends on the placement and number
of electrons in its energy bands. The wider the energy bands of a molecule,
the faster the electrons move; the faster the movement of electrons, the
better the conductivity. Metals generally have wider bands than semiconductors,
which have wider bands than insulators.
Biological DNA shows a band-gap of a few hundred millielectron volts at
room temperature, according to the researchers. This gap is an energy
barrier that any electron coming from the electrode would have to overcome
before it could be conducted up the molecule, said Xu.
In contrast, M-DNA's “conduction band is wide and low enough in energy
that the electrons from the electrode can move into [it] without difficulty,”
This difference makes metallic DNA an ideal nanoscale semiconductor, according
“With semiconductors you have a set of base materials - building blocks
- which can be turned into a vast array of useful devices and sensors,
which, in turn, can be connected up to form circuits, processors, and
computers,” Xu said. The engineered DNA is a new material, “and new materials
are technology enablers,” he said.
Metallic DNA could also be used as a biosensor to screen, among other
things, genetic aberrations and environmental toxins. Metallic DNA could
be used in sensors in 3 to 5 years, Xu said.
“It is interesting work, but I think there still needs to be a lot done
to structurally characterize this system,” said Jacqueline K. Barton,
a professor of chemistry at the California Institute of Technology.
It’s the first time zinc has been studied in this way, said Mark Ratner,
a professor of chemistry at Northwestern University. The work is “an intriguing
and important contribution,” but the other research in the field of conductive
DNA has produced different results. “There is lots yet to be done,” he
Other researchers are more skeptical about the findings. “[Xu and his
colleagues] find a very low gap even for simple [biological] DNA, which
contrasts [with] similar measurements by us and others where we find true
insulating behavior at these length scales,” said Cees Dekker, a professor
of physics at the Delft University of Technology in the Netherlands.
Xu’s research colleagues were Andrei Rakitin, Chris Papadopoulos, and
Yuri Kobzar of Brown University; Palok Aich and Jeremy S. Lee of the University
of Saskatchewan; and Alex S.Vedeneev of the Russian Academy of Sciences.
Their paper appeared in the journal Physical Review Letters, April 16,
The research was funded in part by the Canadian Institute for Advanced
Research, the National Sciences and Engineering Council of Canada, Motorola,
the Defense Advanced Research Projects Agency (DARPA), the Office of Naval
Research, the National Science Foundation, and the Air Force Office of
Timeline: 3 - 5 years
Funding: Government; Corporate
TRN Categories: Biological, Chemical, DNA and Molecular
Story Type: News
Related Elements: Technical paper, " Metallic Conduction
through Engineered DNA: DNA Nanoelectric Building Blocks" appeared in
the journal Physical Review Letters, April 16, 2001.
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