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.

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.

A novel flexible zinc oxide/poly­(vinylidene fluoride) (ZnO/PVDF) nanocomposite was prepared by electrospinning for fabricating a piezoelectric nanogenerator (PNG). The ZnO nanoparticles (NPs) and nanorods (NRs) were used as nanofillers of piezoelectric PVDF to prepare fibrous nanocomposite membranes. It has been found that the addition of piezoelectric ZnO NPs and NRs can improve the overall performance of the PNGs fabricated with the electrospun membranes. A large electrical throughput (open circuit voltage ∼85 V and short circuit current ∼2.2 μA) from the ZnO NR/PVDF fiber membrane-based PNG (ZR-PNG) indicates that ZnO NRs are effective functional fillers for PVDF. The high aspect ratio and flexibility characteristics of ZnO NRs were found to be highly beneficial for improving the piezoelectric properties of the nanocomposites. ZnO NRs act as nucleating agents of β-phase PVDF, and ZnO NRs can also produce piezoelectric charges when they deform with the composite fibrous membrane. It has been concluded that the obvious synergistic effects between the piezoelectric nanofillers and electroactive β-crystals of PVDF in the ZnO NRs/PVDF composites are useful for the construction of the high-performance flexible PNG. In addition, the fabricated ZR-PNG can light up commercial light emitting diodes (40 white, 36 blue) and charge the capacitors in a very short time (3 V is accomplished in 25 s), which indicates the potential of the ZR-PNG for portable, wearable, flexible, or self-powered electronic devices.

Effective quadratic nonlinearities as high as 0.2 pm/V are reported for the first time to our knowledge in poled germanosilicate fibers. This value is ~200 times higher than previously achieved in these fibers. The presence of Ge is found to enhance the efficacy of both thermal (in combination with OH doping) and electron-beam poling in silica.

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Realisation of a device intended for the manipulation and detection of bead-tagged DNA and other bio-molecules is presented. Acoustic radiation forces are used to manipulate polystyrene micro-beads into an optical evanescent field generated by a laser pumped ion-exchanged waveguide. The evanescent field only excites fluorophores brought within ~100 nm of the waveguide, allowing the system to differentiate between targets bound to the beads and those unbound and still held in suspension. The radiation forces are generated in a standing-wave chamber that supports multiple acoustic modes, permitting particles to be both attracted to the waveguide surface and also repelled. To provide further control over particle position, a novel method of switching rapidly between different acoustic modes is demonstrated, through which particles are manipulated into an arbitrary position within the chamber. A novel type of assay is presented: a mixture of streptavidin coated and control beads are driven towards a biotin functionalised surface, then a repulsive force is applied, making it possible to determine which beads became bound to the surface. It is shown that the quarter-wave mode can enhance bead to surface interaction, overcoming potential barriers caused by surface charges. It is demonstrated that by measuring the time of flight of a microsphere across the device the bead size can be determined, providing a means of multiplexing the detection, potentially detecting a range of different target molecules, or varying bead mass.

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