Probing DNA conductivity with photoinduced electron transfer and scanning tunneling microscopy

The possibility that the stacked DNA bases can mediate vectorial electron t ransfer has been examined using two different approaches. Experiments on ph otoinduced electron transfer with intercalated donors and accepters (either randomly bound or linked dyads of ruthenium complex and viologen) indicate that while DNA may be a better medium than acetonitrile for electron trans fer over short distances (2-3-base pair, equivalent to 10-14 Angstrom centr e-to-centre separation), it is a poor medium for transport over larger sepa rations. Attempts to measure conductivity of individual DNA molecules using scanning tunneling microscopy to image mixed monolayers of mercaptohexanol (MCH) and 30-mer or 10-mer DNAs with alkanethiol linkers also indicate tha t DNA in its native state is a poor conductor. AFM images of the DNA/MCH mi xed monolayers show that the DNA molecules extend vertically upward from th e surface in such surface architectures.