Modification of DNA towards high conductance and transport measurements with
controllable electrodes

Prof. Dr. Elke Scheer, University of Konstanz [Homepage]

Prof. Dr. Andreas Marx, University of Konstanz [Homepage]

Dr. Artur Erbe, University of Konstanz

We investigate the electronic transport through synthetic DNA molecules (10 to 30
basepairs) contacted by the mechanically controllable breakjunction technique (MCB) with
covalent bonds to noble metal electrodes enabling us to vary the distance of the electrodes
for the same molecule. The latter is important to investigate the influence of the structure of
the molecules on the transport properties at the very same molecule.
In summary: the goal for the forthcoming funding period is twofold: At first we will
conclude on the most reproducible contacting method, i.e. combination of thiolated-endgroup
of DNA and electrode metal and the most suitable contacting protocol. The second goal is to
clarify the transport mechanism of the DNA molecule in varying conditions. The final goal for
the envisioned third funding period would then be to develop modifications of DNA that result
in high conductance. Possible modifications include so-called G-quadruplexes since they are
supposed to have considerably higher conductance.
An important issue in the transport through DNA is the role of the sequence. A high
electro n-transfer rate is predicted for pure CG (cytosine-guanine) DNA. However, this
sequence is not stable in the usual (B) conformation. We will concentrate on CG-rich, quasiperiodic
sequences for optimizing the conductance behavior.
Another parameter which determines the structure and thus the conductance of DNA
derivates is the chemical environment. We compare the transport behavior of the species in
vacuum, in ambient conditions (dry), in de-ionized water and in physiological buffer solution.
A prerequisite for systematic transport measurements is a reliable contacting scheme,
which we have developed during the first funding period. We will continue these
investigations for revealing the optimum contacting protocol. To be specific, we developed a
reproducible contacting scheme by attaching the linking group to the base thymidine.
Preliminar results of Elstner et al, which have been obtained within this priority program as
well predict higher conductance when linking the base guanine to metal electrodes. We will
pursuit this strategy in the upcoming funding period.
if finally the influence of the contacts and conformation is revealed, DMA-based hybrid
materials will be developed that give rise to high conductance values.