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"Probing the electronic transport properties of individual fullerene-DNA complexes."

Technology is facing a challenge in adapting to the new miniaturization strategies with the current trend of incorporating more computing processes in smaller electronic devices. In this context, we present here an environmentally friendly solution: the use of DNA as electrical nanowires for developing even more complex integrated circuits. The fact that DNA is composed of carbon, phosphor and sugar (deoxyribose), readily available in our daily life makes them an environmentally friendly option. Additionally, the length and complexity of the structure can be easily controlled and, besides DNA in dry state is a very stable molecule. Thus, replacement of semiconductor interconnections (wires) by DNA nanowires would result in a more ecological and cost-effective solution.

However, DNA wires are not yet featured to assemble complex circuits because the nature of electronic transport through DNA is not fully understood. Extensive efforts have been done in this matter without a clear consensus whether DNA behaves as an insulator, conductor or semiconductor. The structural conformation of DNA is believed to play a key role on its electrical behaviour. Thus, keeping the B-DNA structure (native DNA) in dry state is of great importance due to the favourable π-pathway that is formed along the helix, which does not take place in other DNA conformations. Another key factor is the selection of a small electron donor-acceptor group that could aid on the direct flow of charges through the DNA helix, without interfering with the structure. If this group has a strong adsorption to the surface and allows the production of homogeneous molecules (preferably single molecules), then electrical measurements can be performed in a reproducible way.

In this thesis, stable single fullerene-DNA molecules that transport electrical charges exclusively along the DNA have been produced. When charges are injected on DNA [from -1 V to +1 V] a symmetrical-semiconductor I-V profile is displayed, indicating that charges hop along the DNA towards the fullerene ends. A marked tendency was observed, where conductance changed accordingly from semiconductor to conductor, when the DNA distance with respect to the fullerene group was large (194.75 Å) and slowly diminishing to zero.

In addition, the production of single DNA wires connecting gold nanostructures in a dry state, that work at low voltage ranges, could result on more complex integrated circuits (small DNA wires = more interconnections) with a lower range of power supply. This implies that fullerene-DNA molecules could be used for the assembly of a new generation of DNA chips that require only a prior chemical synthesis and direct deposition of molecules on top of tiny gold nanostructures.

Furthermore, another interesting property of these molecules is that fullerenes attached to DNA can display features oriented in nanomedicine, such as photoactivable drugs in photodynamic anticancer therapies, where their on/off switching mechanism could be directly influenced by the charges hopping along the molecule in an aqueous solution.