Direct measurement of electrical transport through DNA molecules

Attempts to infer DNA electron transfer from fluorescence quenching measure ments(1-9) on DNA strands doped with donor and acceptor molecules have spur red intense debate(10,11) over the question of whether or not this importan t biomolecule is able to conduct electrical charges. More recently, first e lectrical transport measurements on micrometre-long DNA 'ropes'(12), and al so on large numbers of DNA molecules in films(13), have indicated that DNA behaves as a good linear conductor. Here we present measurements of electri cal transport through individual 10.4-nm-long, double-stranded poly(G)-poly (C) DNA molecules connected to two metal nanoelectrodes, that indicate, by contrast, large-bandgap semiconducting behaviour. We obtain nonlinear curre nt-voltage curves that exhibit a voltage gap at low applied bias. This is o bserved in air as well as in vacuum down to cryogenic temperatures. The vol tage dependence of the differential conductance exhibits a peak structure, which is suggestive of the charge carrier transport being mediated by the m olecular energy bands of DNA.