**2.1. Electron transfer through DNA**

The deoxyribonucleic acid (DNA) is a biopolymer in a double helical form, which is constituted by an extended array of aromatic π-stacked base pairs adenine-thymine (AT) and guanine-cytosine (GC) within a polyanionic sugar-phosphate backbone (**Figure 2**). Due to the biological implications, the studies about the charge migration in DNA were related to physiological processes: the possibility and efficiency of charge transfer is significant, because the migration of the radical cation is a critical issue to understand problems related to radiation damage and mutation [27, 28].

The role of π-π interactions between stacked base pairs in double-stranded DNA could provide a pathway for rapid one-dimensional charge separation. Various experiments were performed

**Figure 2.** Representations of left (a) truncated octahedron containing six squares and eight hexagons. (b) Each edge of the truncated octahedron contains two double helical turns of DNA a DNA cube containing six different cyclic strands. Their backbones are shown with different colors.

to understand whether DNA facilitates the charge transfer over long distances and whether the base pair stack can act as a conducting medium. The issue of charge migration in DNA has recently become a hot topic with solution chemistry (in particular) after the first reports by Jacqueline Barton's group [29–33] in the early '90s. Although the answer to the question: Is DNA a molecular wire? is still elusive.

The recent achievement is the construction of few DNA-hybrid devices, which requires the application of some state-of-the-art nanotechnologies are: electron beam lithography for the fabrication of metallic nanocontacts, trapping techniques to compel the molecules into the desired device scheme, Atomic Force Microscopy (AFM) or Scanning Tunneling Microscopy (STM) for imaging and probing samples.

The achievement of DNA-based devices requires [33]:


The DNA-based materials may be used either as conductive wires or as a template for other conductive materials. By exploiting the molecular recognition of its functional groups, it is possible to synthetize branched DNA-motifs that may be assembled into periodic arrays. Though a lot of research conducting in this field is giving the contrasting results.

The most important ones are:

**2. DNA biomolecular electronics**

172 Green Electronics

iochemical stability and mechanical rigidity.

**2.1. Electron transfer through DNA**

Their backbones are shown with different colors.

The role of ME is to provide reproducible well-structured architectures, easy to wire in a programmed manner. Supramolecular chemistry seems to fulfill these needs [22]. The two properties which are attractive for this purpose is the (a) molecular recognition and (b) selfassembly. Molecular recognition is the capability of a molecule to form selective bonds with other molecules or with substrates, which rest on the information stored in the structural features of the interacting partners. Molecular recognition processes (a) the building up of the devices from their components (b) incorporate them into supramolecular arrays; (c) allow selective operations on given species (e.g. ions, dopants), and (d) control the response to exter-

The self-assembly has the capability of molecules to spontaneously organize in supramolecular aggregates under well-defined experimental conditions. Self-organization may occur both in solution and in the solid state, and make use of hydrogen bonding, electrostatic donoracceptor effects (Van der Waals, dipolar, etc.) or metal-ion coordination as basic interactions between the components. Due to these two properties, DNA molecules seem particularly suitable to be used as components for the construction of nanometer scale devices [23–26]. The idea of using DNA in molecular devices is its natural function of storing and coding the genetic information. DNA transmits well-defined chemical information through the pairing properties of the bases. In addition, it occurs in a large variety of structures and display phys-

The deoxyribonucleic acid (DNA) is a biopolymer in a double helical form, which is constituted by an extended array of aromatic π-stacked base pairs adenine-thymine (AT) and guanine-cytosine (GC) within a polyanionic sugar-phosphate backbone (**Figure 2**). Due to the biological implications, the studies about the charge migration in DNA were related to physiological processes: the possibility and efficiency of charge transfer is significant, because the migration of the radical cation is a critical issue to understand problems related to radiation damage and mutation [27, 28]. The role of π-π interactions between stacked base pairs in double-stranded DNA could provide a pathway for rapid one-dimensional charge separation. Various experiments were performed

**Figure 2.** Representations of left (a) truncated octahedron containing six squares and eight hexagons. (b) Each edge of the truncated octahedron contains two double helical turns of DNA a DNA cube containing six different cyclic strands.

nal perturbations (e.g. external fields, light, electrons, other molecules, etc.).


Apart from experimental difficulties in the fabrication of DNA-based device, several fundamental questions are still open: what are the interactions which control the electrical properties of DNA? How do they depend upon the sequence? What are the mechanisms for charge transport? What are the effects of dopants or defects? How does DNA attach to a metal electrode? What are the effects of the contacts on the conduction properties of the device?

#### **2.2. Application of DNA in green electronics**

DNA can be used in various applications in green electronics, which is discussed herein.
