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The synthesis of supramolecular conducting nanowires can be achieved by using DNA and pyrrole. Oxidation of pyrrole in DNA-containing solutions yields a material that contains both the cationic polypyrrole (PPy) and the anionic DNA polymers. Intimate interaction of the two polymer chains in the self-assembled nanowires is indicated by FTIR spectroscopy. AFM imaging shows individual nanowires to be continuous, approximately 5 nm high and conformationally flexible. This feature allows them to be aligned by molecular combing in a similar manner to bare DNA and provides a convenient method for fabricating a simple electrical device by stretching DNA/PPy strands across an electrode gap. Current-voltage measurements confirm that the nanowires are conducting, with values typical for a polypyrrole-based material. In contrast to polymerisation of pyrrole on a DNA template in bulk solution, attempts to form similar wires by polymerisation at surface-immobilised DNA do not give a continuous coverage; instead, a beads-on-a-string appearance is observed suggesting that immobilisation inhibits the assembly process.

Polyindole (PIn) nanowires were formed on a lambda-DNA template by chemical oxidation of indole using aqueous FeCl3. The resulting nanowires are smooth, regular, conductive and had diameters in the range of 5-30 nm. These features allow them to be aligned by molecular combing and studied by scanned conductance microscopy, conductive AFM, and two-terminal I-V measurements. Using this combination of measurements, we find that the conductivity of PIn/DNA nanowires is between 2.5 and 40 S cm(-1) at room temperature, which is substantially greater than that in previous reports on the bulk polyindole conductivity (typically 10(-2)-10(-1) S cm(-1)). The conductance at zero bias shows an Arrhenius-type of dependence on temperature over the range of 233 to 373 K, and the values observed upon heating and cooling are repeatable within 5%; this behavior is consistent with a hopping mechanism of conductivity.

Silicon carbide has attracted considerable attention in recent years as a potential material for sensor devices. This paper reviews the current status of SiC technology for a wide range of sensor applications. It is shown that SiC MEMs devices are well-established with operational devices demonstrated at high temperatures (up to 500 °C) for the sensing of motion, acceleration and gas flow. SiC sensors devices using electrical properties as the sensing mechanism have also been demonstrated principally for gas composition and radiation detection and have wide potential use in scientific, medical and combustion monitoring applications.

Confining the growth of semiconductor materials to the low nanometer regime provides access to size quantization phenomena that may be exploited for a range of applications, such as probing intracellular processes, chemical and biological sensing, and nanometer-scale electronics.[1-4] Whilst control over length scales is well-developed for many types of materials, their form (e.g., dimensionality) and subsequent organization into hierarchical and functional systems remains challenging. One approach that is proving successful in addressing these problems is the use of biopolymers as templates, scaffolds, and interconnects. [5][6][7][8][9][10] DNA has been particularly effective in this regard and has been used to grow and/ or organize both inorganic (e.g., CdS, ZnS) [11][12][13][14][15][16][17] and molecular-based (e.g., polyaniline) semiconductor materials. [18][19][20] Here, we report the use of DNA strands, both surface-immobilized and in solution, to template the growth and organization of the binary semiconductor CdS. Through careful optimization of the reaction conditions and the state of the DNA, we have been able to control the reaction and prepare quantum-confined CdS as either 1D chainlike assemblies of particles or as uniform nanowires. The latter were subsequently integrated into a simple two-terminal electrical device to demonstrate the utility of these materials as possible nanometerscale electronic components.Reactions of cadmium and sulfide ions on surface-bound DNA employed two different surface types: mica, and alkyl monolayers on single-crystal Si(111). The mica surfaces allowed the DNA molecules to be anchored via interactions between the metal ions, the surface oxygen functionalities, and the phosphate groups. The alkyl monolayers on Si(111) provide an inert, flat surface on which DNA may be conveniently aligned by combing. [21,22] On mica substrates k-DNA was spotted onto a freshly cleaved surface and allowed to incubate with Cd(NO 3 ) 2 for 10 min. at room temperature. After rinsing, the surface was treated with a solution of 1 mM Na 2 S. Initially aqueous sulfide solutions were used, but in these cases rapid precipitation occurred and randomly deposited material was observed. Instead, treatment with 1 mM Na 2 S in a 1:1 water/ethanol mixture (v/v) gave the desired selective growth of CdS on the DNA template. Figure 1 shows a typical atomic force microscopy (AFM) image of the surface after reaction.Nanoparticles can be seen adhering on the DNA strands, resulting in a beads-on-a-chain appearance. The particles are also highly monodisperse, with diameters (width data) in the range 11.3-16.7(±1.4) nm (average 14.2 nm ± 10 %). Furthermore, there is a notable registry of the particles along the length of some of the polymer chains. In marked contrast, reactions at DNA that had been aligned through combing onto alkylated Si(111) produced material that was much less regular in appearance. After reaction, the surface was found to contain randomly coiled strands, indicating that the DNA is mobile dur...

Polypyrrole nanowires formed by polymerization of pyrrole on a DNA template self‐assemble into rope‐like structures. These ‘nanoropes’ may be quite smooth (diameters 5–30 nm) or may show frayed ends where individual strands are visible. A combination of electric force microscopy, conductive atomic force microscopy and two‐terminal current–voltage measurements show that they are conductive. Nanoropes adhere more weakly to hydrophobic surfaces prepared by silanization of SiO2 than to the clean oxide; this effect can be used to aid the combing of the nanoropes across microelectrode devices for electrical characterization.

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