DNA Structure on Electrode Surfaces

The adsorption of dsDNA onto gold electrode surfaces shown by STM and AFM images obtained by Lindsay et al. [83-86] demonstrates that DNA molecules adsorb on the surface reversibly and can undergo conformation transitions. Additionally, the electrochemical deposition and in situ potential control during imaging can be used to obtain reproducible STM images of the internal structure of adsorbed ssDNA and dsDNA. Spectroscopic techniques... 

The double-strand structure of an oligonucleotide is shown schematically in Fig. 6-1. Anticipating discussion in later Sections, the molecule is shown in a upright orientation attached to an atomically planar metallic electrode surface (Au(lll), cf below) by chemisorption via a hexamethylenethiol group. Fig. 6-1 shows the four nucleobases presently in focus. We discuss first concepts and formalism of electron and hole transport of DNA-based molecules in homogeneous solution and at electrochemical interfaces. We then focus on DNA-based molecules in electrochemical nanogaps and STM in electrochemical environments in situ STM). Some case examples illustrate accordance and limitations of current theoretical views of DNA-conductivity. This adds to the comprehensive overview of interfacial electrochemical ET of DNA-based molecules by O Kelly and Hill in Chapter 5. 

Single-molecule resolution has been achieved for redox metalloproteins, larger redox metalloenz5mies, and DNA-based molecules in surface-confined monolayers on metallic electrode surfaces, where the biological function in natural aqueous environment can be controlled by the electroehemical potential. Not only structural mapping of immobilized redox metalloproteins and DNA-based molecules can be achieved. Given adequate theoretical support, ET and redox enzyme function can also be addressed at this level of resolution. The Os-complexes and the redox... 

The DNA duplex can be considered as a stacked-pi system, and there has been a long debate on the possibility of electron transfer through such a molecular structure (Fink and Schonenberger, 1999 Kelley et al., 1999 Ye and Jiang, 2000). It is clear, meanwhile, that DNA can effectively transport electrons under defined conditions, but it is critical to achieve this situation at an electrode. However, disregarding the pathway of electron transfer, DNA-bound redox labels can be detected sensitively at the electrode and thus used for the indication of hybridization. Alternatively, the charge distribution altered by the hybridization can be detected by impedance spectroscopy analyzing the interfacial properties of an electrode surface. 

The structural changes in redox-modified single-chain DNA have been applied in electrochemical biosensors. In one example, a hairpin structure on an electrode snrface places the ferrocene label on its free 5 end in close proximity to the electrode, thus allowing a constant electron flow (Fan et al., 2003). Hybridization with its target DNA leads to formation of the duplex, in which the distance between the redox label and the electrode surface is increased beyond the possibility of electron transfer. 

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