The
ever increasing miniaturization of electronics has encouraged researchers
to study conductors at the nanometric scale, to find the thinnest
wire imaginable - single molecules. Until recently, experiments on
conduction through DNA molecules have given contradictory results.
Recently, however, researchers at the Solid Physics Laboratory in
Orsay ("Laboratoire de physique des solides", CNRS-Université
Paris 11), and the Moscow Academy of Science have observed conduction
through a DNA molecule stretched across a 0.5 micron gap separating
two metallic electrodes. The difficulty in attaching the ends of the
DNA molecule to the electrodes seems to be at the root of the contradictions
between previous reports. Very often, the connections form "tunnel
junctions" which have a resistance that varies enormously from
one sample to another. The material used to make the connection is
therefore crucial. Rather than using gold, researchers in Orsay and
Moscow chose a combination of carbon and a superconducting metal,
Rhenium.
Under
these conditions, DNA was found to be a conductor nearly as efficient
as copper. The resistance was approximately 20 kilo Ohms at room temperature
- the best conductance so far observed for DNA. Cooling down to one
Kelvin (1K) had little effect on conductivity, but below 1K, the critical
temperature, the researchers were surprised to observe superconductivity
in the DNA wire, induced by the Rhenium electrodes.
