We investigate the electronic transport through synthetic DNA molecules contacted by the mechanically controllable breakjunction technique (MCB) with thiol bonds to gold electrodes. This allows on the one hand to use short sequences (10 bo 30 basepairs) which is favorable to have a measurable current and on the other hand to vary the distance of the electrodes for the same molecules. The latter is important to investigate the influence of the structure of the molecules on the transport properties at the very same molecule. With special linking arms, part of the conformational changes can be suppressed (so-called LNA: locked DNA). Measurements on LNA will serve as reference for the unlocked DNA.
An important issue in the transport through DNA is the role of the sequence. Competing theoretical models predict different sequences that should be favorable. A high electron transfer rate is predicted for pure CG (cytosine-guanine) DNA. However, this sequence is not stable in the usual confirmation. Pure AT (adenine-thymine) DNA has been shown experimentally to have no significant conformational change while the predictions for charge transport are contradictory. We will investigate systematically different sequences.
In the light of existing experiments natural DNA appears to be too resistive to serve as conductors in molecular electronics. However, the methods to create synthetic DNA with arbitrary sequence are very elevated. Consequently, if finally the influence of the contacts and conformation is revealed, DNA-based hybrid materials will be developed that give rise to high conductance values.
In summary: the goal of the project is threefold. At first we want to clarify the tranport mechanism of the DNA molecule. A prerequisite for this aim is to find a suitable, reproducible contacting method (goal 2). The third and final goal would then be to develop modifications of DNA that result in high conductance.