Superconductivity: it's in the genes
Jan 12, 2001
In the quest for ever-smaller electronic devices, scientists have long dreamt of building circuits up atom by atom. But finding molecules capable of conducting electric current has not been easy. Now, Alik Kasumov of the Laboratoire de Physique des Solides in France and co-workers have shown that DNA molecules act as ohmic conductors above 1 K and that below this temperature they can superconduct (A Y Kasumov et al 2001 Science 291 280).
Following on from the discovery that carbon nanotubes can act as electrical wires, Kasumov showed two years ago that these rolled up sheets of graphite atoms lose their resistance when connected to superconductors. Now Kasumov has shown that this is also true for DNA by connecting double-stranded DNA molecules to rhenium and carbon superconducting electrodes 0.5 µm apart. By cooling the electrodes to below their superconducting transition temperatures, the researchers observed so-called 'proximity induced' superconductivity in the DNA.
Evidence for electrical conductivity in DNA molecules has been inconclusive until now. Optical experiments have shown that a transfer of charge may be possible in such molecules. But the message from transport measurements has been mixed: some have indicated that DNA could be a conductor while others suggested that DNA is an insulator. Kasumov and colleagues have found that above 1 K, the resistance per molecule is less than 100 kilo-ohm, a figure that varies weakly with temperature and is an order of magnitude lower than previous measurements. Even at very low temperatures, the researchers found that DNA molecules can conduct ohmically over distances of a few hundred nanometres.
However, the physical mechanism responsible for conduction in DNA remains unclear and it is possible that the contacts act as strong dopants of electrons or holes. The researchers add that conductivity measurements could in turn help biologists to look for particular sequences of base pairs within DNA molecules.