The charge transport mechanisms in DNA proposed in the literature cover broad range of possibilities including molecular band conduction, superexchange, multistep hole hopping, and polaron hopping. The reason for the surprisingly diverse results is all the variables in the experiments - DNA sequence, DNA characteristic (single molecule or bundle, DNA length), the metal/DNA contacts, and the environmental dissimilarities in temperature, humidity, etc.

In this study, the humidity effect on the electrical conduction in DNA was systematically investigated in a humidity chamber over the wide range of DC voltage. The exponential increase in conduction with increasing humidity was observed for the natural DNA thin-film, and it was attributed to the protonic conduction by the electrolysis of water. In addition, the negative differential resistance was measured in highly hydrated DNA films. The detailed analysis revealed that it was caused by the slow diffusion of water molecules on the surface of DNA molecules.