Conductivity of DNA

The natural conductivity of DNA and the potential means for its improvement have recently been re-evaluated [54,55]. Use of DNA bridges for nano-wiring appears very attractive in view of the recent great achievements in the design, control, and fabrication of DNA-made nanostructures [5]. It appears, however, that the conversion of DNA wires into effective nano-conductors is still a major problem. 

Okahata Y, Kawasaki T (2005) Preparation and Electron Conductivity of DNA-Aligned Cast and LB Films from DNA-Lipid Complexes. 260 57-75 Otto D, see Ihmels H (2005) 258 161-204... 

Preparation and Electron Conductivity of DNA-Aligned Cast and LB Films from DNA-Lipid Complexes... 

This past decade has seen numerous controversial studies regarding electrical conduction of DNA. Some reported high conductivity [115, 116, 118] with Crt of at most lO" S cm [115] or even superconducting properties [119], while others claimed that the carefully deionized DNA molecules are insulating [117, 120] in agreement with the old reports [121, 122] with ctri- less than 10 S cm. The controversy seems to have settled on a wide consensus that, apart from ionic conduction by the sodium gegenions, double-stranded DNA is an electrical insulator. 

Unlike direct measurements of electrical conductivity of DNA [34, 35], chemical and photochemical experiments provide detailed data on how the CT efficiency depends on the DNA sequence and the local structure of an oligomer [5-9]. The latter experiments rely on intercalated or covalently bound chromophores which may affect the DNA structure. In the following, we will not discuss this effect of the chromophore although we realize that it may be important for a complete description of the systems used in those experiments. Rather, we will focus on a better understanding of the CT through unperturbed DNA fragments. 

Recently, the effects of static and dynamic structural fluctuations on the electron hole mobility in DNA were studied using a time-dependent self-consistent field method [33]. The motion of holes was coupled to fluctuations of two step parameters of a duplex, rise and twist (Fig. 1), namely the distances and the dihedral angles between base pairs, respectively. The hole mobility in an ideally ordered poly(G)-poly(C) duplex was found to be decreased by two orders of magnitude due to twisting of base pairs and static energy disorder. A hole mobility of 0.1 cm V s was predicted for a homogeneous system the mobility of natural duplexes is expected to be much lower [33]. In this context, one can mention several theoretical studies, based on band structure approaches, to estimate the electrical conductivity of DNA [85-87]. 

When the relatively low conductivity of DNA was acknowledged, there were suggestions that DNA be doped to increase its conductivity. It is immediately apparent that the methods used for doping conjugated polymers, which led... 

The two approaches are not unrelated and a complementary analysis of both kinds of studies would finally shed light onto the detailed mechanisms for charge migration along DNA wires [51]. The kinetic theories are reviewed in other chapters of this book. Here, we focus on results obtained for the electronic structure of extended DNA base stacks, and describe their influence on the electrical conductivity of DNA-based nanostructures. 

Finally, transport in bio-molecules attracted more attention, in particular electrical conductance of DNA [286-290]. 

The use of DNA molecules as wires in electronic systems may open a new opportunity in nanoelectronics. DNA has the appropriate molecular recognition features and well-characterized self-assembly. There is evidence to suggest that DNA is only a marginally better electron conductor than proteins [116-118], As a result, many studies have focused on various methods of DNA modification leading to improvement in its conductive properties. It is possible to enhance the conductivity of DNA by coating it with a thin film of metal atoms, but the molecular recognition properties of the DNA are then destroyed. An effective approach to this problem is the incorporation of metal ions into the DNA double helix [118-121], Preliminary results suggest that a metal ion-DNA complex may be a much better conductor than B-DNA, because the former shows a metallic conduction whereas the latter behaves like a wide-band gap semiconductor [118]. 

Evidence of the electrical conductivity of DNA and of its important mechanisms has been discussed for a long time and has led to a theory of electron conduction in biopolymers [25, 82]. From this it appeared that the major carrier of conductivity is either electronic or ionic, depending on the temperature of the sample, the water content, and the fact that the conductivity of native samples is higher than that of denatured samples. Following electrochemical oxidation of dsDNA and ssDNA in electrolyte solutions over a wide range of pH, interesting electrochemical properties of a glassy carbon electrode with dsDNA or ssDNA adsorbed on the electrode surface were observed [68]. 

Figure 28.5 Effects of added ionic liquid concentration on the ionic conductivities of DNA BFy C- TFSI (A) and DNA - BF4/ EI1VBF4 (%) atSCFC. Those of pure C TFSI (A) and pure ElmBF4 (O) are also depicted as references.

In this chapter we reviewed our work on preparing ion conductive films by using DNA. The highest ionic conductivity of 5.05 x 10 S cm was found to be at 50°C when 93 wt% EImBF4 is mixed with DNA neutralized with HBF4. The DNA film was obtained by casting a DNA aqueous solution. The attractive characteristics of DNA is that it is a biodegradable material that has an inexhaustible supply in nature. We showed in this chapter that several properties, such as ionic conductivity of DNA films, can be controlled by certain factors. It is our hope that our results well open the way to new applications of DNA. 

Juyeon Yi, Conduction of DNA molecules A charge-ladder model. Physical Review B, 68, 193103-1 (2003). 

The chapter by Hill and Kelley addresses the interfacial electronic conductivity of DNA-based molecules controlled by the electrochemical potential. Binding of redox probes is a probe for electronic communication between the probe and the electrode through the DNA-molecular frame and therefore of the tunneling conductivity of the latter. This remains an intriguing issue as the redox-based electronic energies of the nucleobases are strongly off-rcsonance with the electrode Fermi energy and the redox level of the probe molecule. 

High-energy radical states are also likely to be involved in onedimensional single-molecule (or a few molecules) conductivity of DNA-based molecules in solid state configurations where the molecules are immobilized... 

In addition to the fundamental importance of electronic conductivity of molecules as intriguing as DNA and proteins, electronic conductivity of DNA-based molecules holds other perspectives. Charge transfer along the DNA double-strand has been forwarded as an in vivo mechanism for radiation and chemical damage of the DNA-based genetic system, and for... 

The hopping conductivity scheme above represents formally the data for in situ STM imaging and up to a point single-molecule conductivity of DNA-based molecules as observed. The issues of the energetics and the nature of the charge (electron or hope) transmitting states are, however, left open. 

The conductance of DNA molecular wires has been measured by both the methods of Xu et al. and Haiss et Both these methods rely on the... 

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