**2. Electrical characterization of DNA-based metallic nanowires**

Novel conductive DNA-based nanomaterial, DNA-peptide wire composed of a DNA core and a peripheral peptide layer, is used for the wide variety of nano electronic and biosensor applications. The electrical conductivity of these wires is higher than the native double-stranded DNA (dsDNA). These wires produce high conductivity and better resistance to the mechanical deformations caused by the interactions between the substrate and electrode surface. Porath et al. [38] has studied the electrical transport through short (10 nm) dsDNA molecules deposited between platinum nanoelectrodes at different temperatures, confirming the reproducible semiconducting behavior with a gap [39, 40].

Electrical studies indicate that the charge transport in DNA is dominated by holes due to the position of the HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) levels of DNA with respect to the Fermi energy of the coinage metal contacts (e.g., Au and Pt), though the photo physical studies indicate the transportation of both hole and electron in DNA [41]. As a result, DNA molecule behaves as a p-type nanowire [42]. The representation of conductive silver nanowires and nanoparticles NPs attached on the DNA origami are given in **Figure 3**.

The charge transport is explained by three main mechanisms: single-stepelectron-tunnelling, thermal hopping, and domain hopping [43]. The charge transport in DNA occurs predominantly through the guanine bases due to their lowest electrochemical oxidation potential. When the DNA is absorbed on the surface, the conformations are affected by the van der Waals, electrostatic, and hydrophobic interactions within the substrate. Further the behaviour of DNA is

## **Figure 3.**

*(a) The construction of conductive silver nanowires, (b) PVD metal deposition on the alignment of DNA NW, (c) RNA functionalized AuNPs and (d) (1) DNA origami molds with Au nanoparticles and (2) nanoparticles NPs attached on the DNA origami. Adapted from Ref. [40].*

affected by the DNA sequences, substrate and contact properties, temperature and humidity [44–46]. Recently, studies were conducted on the electrical measurements on guanine quadruplex DNA (G4-DNA), which is uniform in composition, consist of only G-nucleotides and it was observed that G4-DNA exhibit a greater bending rigidity compared to the dsDNA. Several techniques have been developed for contacting the nanowires with the combination of bottom-up and top-down strategies. These are:

