Transport properties of carrier-injected DNA

We have studied electric properties of carrier-injected deoxyribonucleic acid (DNA) molecules. First, a current ${\mathrm{(I}}_{\mathrm{CA}})$ through a single DNA molecule was measured by the two-probe dc method with varying a distance between a cathode and an anode ${\mathrm{(d}}_{\mathrm{CA}}\mathrm{).}$ The $I_{\mathrm{CA}}{\mathrm{–d}}_{\mathrm{CA}}$ curve showed that the current rapidly decreased with increasing $d_{\mathrm{CA}}$ ${\mathrm{(I}}_{\mathrm{CA}}\text{≲0.1\hspace{0.17em}}\mathrm{nA}$ for $d_{\mathrm{CA}}\text{≳6\hspace{0.17em}}\mathrm{nm})$ 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 ${\mathrm{(d}}_{\mathrm{DS}}\text{)∼20\hspace{0.17em}}\mathrm{nm}.$ When a voltage was applied to the gate, the source–drain current ${\mathrm{(I}}_{\mathrm{DS}})$ 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 $d_{\mathrm{DS}}\text{∼20\hspace{0.17em}}\mathrm{nm}.$ 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 ${\mathrm{(p}}_{\mathrm{GC}})$ in a DNA double strand. We measured the current–voltage curves of DACD for various $p_{\mathrm{GC}}.$ The conductivity of DACD increased nonlinearly with an increase in $p_{\mathrm{GC}}.$ We explained this behavior using a percolation model, so that a two-dimensional conductive network would form in DACD.