Bioactive Devices for Technological Applications

**3**

**Chapter 1**

Nanowires

*Ruby Srivastava*

**1. Introduction**

Introductory Chapter: DNA as

The integration of nanotechnology with biology and bioengineering has produced many advances with the manipulation of well-defined structures at the nanoscale with high accuracy. DNA molecules can be used for the assembly of devices, for the interconnect joints, or as the device element itself. Sequencespecific DNA detection has been applied in the diagnosis of pathogenic and genetic diseases. The unique physical properties of dots or wires with the remarkable recognition capabilities of DNA could lead to the miniaturization of biological electronics and optical devices, which includes the biosensors and probes. Numerous advantages of nano- and micro-biodevices include the separation technologies, HPLC and capillary electrophoretic separation of DNA, nanopillar devices for the ultra-fast separation of DNA and proteins, nanoball materials for the fast separation of wide range of DNA fragments and the nanowire devices for ultra-fast separation of DNA, RNA, and proteins. The studies about these devices have been carried out by *Prof. Yoshinobu Baba* and the research group [1–12]. The nanopillar, nanowall, nanoslit, and nanopore structures were designed by the top down or semiconductor nano-fabrication technology, while the nanoball, nanowire, nanoparticles and the quantum dot structures are designed by the use of bottom up or self-assembled

nano-fabrication technology. These devices are shown in **Figure 1**.

DNA exhibits many other properties; as high stability, adjustable conductance, vast information storage, self-organising capability and programmability. So it is considered as an ideal material for the applications of nanodevices, nanoelectronics and molecular computing. There are several advantages to use DNA for these device designs. The first step of the DNA-based nanotechnology is to attach DNA molecules to the surfaces. It can be done by three different methods: by electrostatic interaction between DNA and a substrate, covalent binding of a chemical group attached to the DNA end and the binding of protein attached at the DNA end to the corresponding antibody immobilized at the surface. Seeman and co-workers [13] have exploited the properties of DNA's molecular recognition to design complex mesoscopic structures based solely on DNA. They used the branched DNA to form stick figures by properly choosing the sequence of the complementary strands. Further macrocycles, DNA quadrilateral, DNA knots, Holliday junctions, and other periodic crystal structures were also designed. DNA-mediated self-assembly of nanostructures has been extended to metallic nanowires [14–16]. In a study, DNA as a template was used to grow conducting silver nanowires [14]. The fabrication of gold and silver wires was used with the DNA as a template or skeleton [15]. Nguyen et al. developed an approach for the attachment of DNA to oxidatively open the ends of multiwall carbon nanotube arrays [17]. The carbon wall nanotubes can be used as electrodes to transmit electrical signals or as sensors to detect the concentration of chemical or
