Electronic conduction in DNA attached to gold electrodes

Experimental studies of electronic conduction in DNA have produced widely varying electronic properties and the debate is open on DNA electron transfer/transport mechanisms. We have advanced work towards quantifying the electrical conductivity of DNA oligonucleotides by ´studying the conductivity of double stranded DNA that is immobilized in a well defined manner in break junctions. To this end an 18 base pair long (approx. 5 nm) guanine rich double stranded DNA molecule has been designed to be attached to gold electrodes. The oligonucleotides used here have been synthesized using thiol (-SH) end groups that can form strong bonds to gold surfaces, and thus should provide low-resistance coupling to the electrodes. For a number of devices, conductivity between the contact pads increases significantly following exposure to a solution containing the DNA double strands. This increase in conductivity is thought to be due to electronic conduction through DNA double strands which are bonded to the two contacts. This hypothesis is confirmed by the loss in conductivity that is measured upon the denaturation of the double strand in deionized water.