Transport properties of carrier-injected DNA

Abstract

We have studied electric properties of carrier-injected deoxyribonucleic acid (DNA) molecules. First, a current (ICA) through a single DNA molecule was measured by the two-probe dc method with varying a distance between a cathode and an anode (dCA). The ICA–dCA curve showed that the current rapidly decreased with increasing dCA (ICA≲0.1 nA for dCA≳6 nm) according to a hopping model. Next, we measured electric properties of DNA injected carriers by two methods; a field effect transistor (FET) arrangement and a chemical doping. In the FET arrangement, we set three electrodes on a single DNA molecule as source, drain, and gate electrodes with a source–drain distance (dDS)∼20 nm. When a voltage was applied to the gate, the source–drain current (IDS) could be detected to be 0.5–2 nA. This showed that charge injection with the FET arrangement would yield a carrier transportation through DNA at least dDS∼20 nm. In order to flow a current through DNA over a distance ∼100 μm, we synthesized the DNA-acceptor cross-linked derivatives (DACD). In the structure of DACD, DNA molecules, which were attached acceptor molecules at guanine sites specifically, were cross-linked by linker molecules. We can modulate the carrier concentration in DACD with changing a guanine–cytosine pair content (pGC) in a DNA double strand. We measured the current–voltage curves of DACD for various pGC. The conductivity of DACD increased nonlinearly with an increase in pGC. We explained this behavior using a percolation model, so that a two-dimensional conductive network would form in DACD.