Modified DNA (M-DNA) was discovered in 1993 by Lee and colleagues . It was found that the addition see more of zinc or other divalent metal ions such as cobalt and nickel raised the thermal denaturing temperature at a high pH of 9. The addition of zinc at high pH suggested that a new conformation was formed. This structure is a good conductor compared to B-DNA molecules as the M-DNA duplex is a chain of metals surrounded by an organic sheet and, hence, capable
of electron transport. Thus, M-DNA can be considered as a nanowire . Figure 8 is a representation of a scanning electron microscopic image of a nanowire made up entirely of DNA . Figure 8 SEM image of DNA template nanowires. DNA is used as a template to produce horizontal nanowires. Here, DNA is tagged with a metal such as gold to produce nanowires through self-assembly while being coated onto a niobium oxide surface . Fink and Schönenberger extended this rationale to a single DNA rope which consisted of a few molecules. They measured the current conducted through the DNA with a potential applied across the DNA under high-vacuum conditions at room temperature as shown in Figure 9. The charge selleckchem transport mechanism NVP-BSK805 order was, thus, determined to be electronic in nature . In another experiment by Porath and colleagues, the voltage applied across the DNA was about 4 V between two platinum nanoelectrodes, and the resulting current did not surpass 1 pA below the
threshold voltage of a few volts. This showed that the system behaved as an insulator at low bias. However, beyond the threshold, the current sharply increased indicating that DNA could transport charge carriers . Figure 9 A qubit made of one short DNA strand attached to two long strands by two H-bonds. The long strands are metal-coated and connected to an external voltage source, Isoconazole V, via resistance, R, and inductance, L. Various spectroscopic methods were also used to investigate DNA conductivity. The movement of electrons was detected at the level
of single molecules by fluorescence decay. Varying fluorescence levels indicated how electrons may have been transferred along the DNA chains [68, 69]. Contact methods can be used to measure conductivity directly. Molecules are laid directly on top of gold electrodes, and current flowing across these circuits is plotted on a graph to ascertain levels of conductivity. However, with this method, it is often difficult to determine whether DNA molecules are in direct physical contact with the electrodes. It is thought that weak physical contact between the DNA and electrode produces an insulating effect and, thus, accounts for varying resistance across the circuit. An expansion in experimental methodology to measure conductivity by a contactless approach will improve understanding of this process . Recently, researchers have been able to develop electrical units besides wires, such as DNA-based transistors [67, 71].