Measurement of electrical transport along stretched λ-DNA molecules using the four-probe method

We have measured the electrical transport along individual λ-DNA molecules stretched across a set of parallel nanoelectrodes using the four-probe method. Up to a relative humidity (RH) of 78%, we find no evidence for electrical transport along λ-DNAs. However, for RHs above 79%, we measure considerable current. The electrical conductance of λ-DNA increases exponentially with increasing RH. For a long λ-DNA molecule with a random base sequence, our results indicate that the current flows through dense water layers surrounding DNA and is dominated by ion transport rather than by electron transport through λ-DNA itself.