Errez Shapir

Scanning Tunneling Spectroscopy of Single DNA Molecules

We briefly present the results of recent experiments of transverse scanning tunneling spectroscopy of homogeneous poly(dG)-poly(dC) DNA molecules and discuss them in the light of theoretical investigation. A semiempirical theoretical model is adopted to describe the transverse tunneling current across a DNA molecule placed between a metallic gold substrate and a metallic STM tip. We show that the main trends in the positions and relative magnitudes of the conductance peaks can be explained by a minimal model of a double tunnel junction with the molecule-electrode couplings and the applied voltage explicitly taken into account.

Energy Gap Reduction in DNA by Complexation with Metal Ions

The electrical properties of single double-stranded DNA (dsDNA) molecules, and in particular conductivity through dsDNA, have several implications in the contexts of biology and nanotechnology. This importance led to a series of investigations [ 1 − 3 ] into the conduction properties and the conduction mechanisms through this 1D wire. [ 4 – 6 ] To expand our fi ndings on dsDNA [ 7 ] , we report comparative scanning tunneling spectroscopy (STS) results showing an interesting consistent discrepancy in the gap width between the dsDNA and the corresponding dsDNA complexed with metal ions (M-DNA). [ 8 ] Electronic structure calculations support the data. The STS study of this novel DNA-based molecule has high scientifi c and technological signifi cance and nicely complements other work in this fi eld, [ 7 , 9–13 ] which was limited to the canonical dsDNA. A poly(dG)-poly(dC) DNA sample was deposited on a gold substrate by electrostatic attraction. Right after the deposition the sample was imaged using atomic force microscopy (AFM) to inspect the DNA topography and to measure the concentration of the molecules on the surface, which was detected as ≈ 1–10 molecules in 1 × 1 μ m 2 . The sample was then inserted into the scanning tunneling microscopy (STM) ultrahigh vacuum (UHV) chamber for measurement. M-DNA molecules were obtained by dipping a DNA sample in a Cu + -ion solution. AFM images were fi rst recorded right after poly(dG)-poly(dC) deposition and then again after metallization of the sample, just before inserting into the UHV chamber. The AFM images show that the surface remains rather clean after the metallization procedure. Figure 1 shows images of DNA and M-DNA molecules scanned at room temperature (RT). Figure 1 a shows an example