We investigate the conductivity of single-stranded and double-stranded herring deoxyribose nucleic acid (DNA) in buffer solution spotted and dried on Au nanocontacts. We find an exponential increase of the conductivity with increasing humidity that is identical for single- and double-stranded DNA within the measurement accuracy. While the small conductivity of dry DNA is comparable to that of a large band-gap semiconductor, we attribute the increase at high humidity levels to water molecules accumulated at the phosphate backbone. For high humidities we observe s-shaped current-voltage characteristics that can be well explained by the dissociation of water attached to the DNA molecules.

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We do not want to state here that DNA is a semiconductor. Further investigations on dry DNA would be needed to support such a statement.

24.

After changing the humidity it is important to wait at least 60min in order to reach an equilibrium.

25.

Note, that this supports the above conclusion of the conductivity mainly arising from the adsorbed water layer and not from the DNA itself.

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