Absence of dc-conductivity in lambda-DNA

The electrical conductivity of biomaterials on a molecular scale is of fund amental interest in the life sciences. We perform first principles electron ic structure calculations, which clearly indicate that A-DNA chains should present large resistance values. We also present two direct procedures to m easure electrical currents through DNA molecules adsorbed on mica. The lowe r limit for the resistivity is 10(6) Ohm . cm, in agreement with our calcul ations. We also show that low energy electron bombardment induces a rapid c ontamination and dramatically affects the measured conductivity, thus provi ding an explanation to recent reports of high DNA conductivity.