Spatial manipulation and ability to assemble and position nanostructures in a controlled manner so they are registered to lithographically defined contacts is a critical step toward scalable integration in high-density nanodevices. By integrating ferromagnetic ends on nanostructures and using the magnetic interaction between ferromagnetic ends and electrodes, we demonstrated assembling, positioning, and spatial manipulating of nanostructures on ferromagnetic contacts. Segmented nickel/gold/nickel (Ni/Au/Ni) and nickel/bismuth/nickel (Ni/Bi/Ni) nanowires with controlled dimensions were fabricated by template-directed electrodeposition. One hundred percent magnetic alignment of nanostructures to the imposed magnetic fields was achieved by applying a low external magnetic field of 200 Oe. In addition, directional controllability of the magnetic assembling technique was demonstrated by assembling nanostructures with angles from 45° to 135° with respect to the electrodes. This magnetic assembly technique was shown to have potential for high-density interconnects without registration and individually addressable nanostructures with the use of different substrate architectures for two-dimensional control of nanostructures placement.

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Conducting polymer nanostructures are emerging materials with tremendous potential for conductometric/field effect transistor (FET) bio/chemical sensors because of their chemical sensitivity and biocompatibility. Herein, we review recent developments in conducting polymer nanowire-based sensors and discuss the impact of several milestones and continuing challenges. Particular attention is given to device fabrication, nanostructure performance enhancement, and functionalization schemes. Several assembly and integration techniques have been developed for single nanowire devices but significant progress is still needed to improve scalability and manufacturability. Future work should focus on high throughput approaches that enable combinatorial screening of conducting polymer nanowires and heterogeneous, high density arrays of conducting polymer nanostructures, deterministically tailored for targeted analytes. The spatial and temporal resolution of conducting polymer nanowires is addressed along with the origin of the sensitivity enhancement. Functionalization routes add another degree of complexity for biosensors and are discussed in the context of nanosensor performance and device fabrication.

Magnetic alignment is reported as a facile technique for assembling nanowires into hierarchical structures. Cross junction and T junction nanowire networks are demonstrated using a sequential alignment technique on unpatterned substrates and predefined lithographically patterned ferromagnetic electrodes. The formation of T junctions prevails as nanowires from the first alignment behave as ferromagnetic electrodes under the external magnetic field of the second alignment. The presence of prefabricated ferromagnetic electrodes dominates dipole interactions of localized nanowires for preferential alignment. Application of a magnetic field from a cylindrical coaxial magnet has also been utilized to form radially aligned nanowires. The magnetic field of the coaxial cylindrical magnet produced a dense, concentric nanowire configuration at the centre of the magnetic field as a consequence of the radial field gradient, and sparse nanowire arrangements in the peripheral field, which were utilized as interconnects with a concentric electrode design.