Conductivity measurements of single DNA molecules using conductive- atomic force microscopy

DNA molecules possess structure and molecular recognition properties that make them excellent candidates for molecular electronics. Understanding the mechanism of charge transport along DNA is an essential step for developing DNA-based molecular electronics. In the experiments reported in this thesis, we applied the method developed by Cui et al. (self-assembled nano-junctions and conductive-AFM) to study DNA molecules. Double-stranded DNA (dsDNA) molecules were integrated between a gold substrate and gold nanoparticles (GNPs). We then use conductive-atomic force microscopy to study the conductivity of single dsDNA molecules labeled by the GNPs. We conclude that DNA molecules have semi-conductor characteristics, with a large band gap. In addition, we showed that an observed asymmetry of the current-voltage curves does not result from the DNA sequence. We propose instead a mechanism of conformation switching between "standing" and "lying" states of dsDNA molecules that arises because of the intrinsic negative charges on DNA strands.