The fire beetle, Melanophila acuminata (Coleoptera: Buprestidae), senses infrared radiation at wavelengths of 3 and 10–25 microns via specialized protein-containing sensilla. Although the protein denatures outside of a biological system, this detection mechanism has inspired our bottom-up approach to produce single zinc phosphide microwires via vapour transport for IR sensing. The Zn3P2 microwires were immobilized and electrical contact was made by dielectrophoresis. Photoconductivity measurements have been extended to the near IR range, spanning the Zn3P2 band gaps. Purity and integrity of the Zn3P2 microwires including infrared light scattering properties were confirmed by infrared transmission microscopy. This biomimetic microwire shows promise for infrared chip development.

Electrical and optical properties of semiconducting nanowires (NWs) strongly depend on their diameters. Therefore, a precise knowledge of their diameters is essential for any kind of device integration. Here, we present an optical method based on dark field optical microscopy to easily determine the diameters of individual NWs with an accuracy of a few nanometers and thus a relative error of less than 10%. The underlying physical principle of this method is that strong Mie resonances dominate the optical scattering spectra of most semiconducting NWs and can thus be exploited. The feasibility of this method is demonstrated using GaAs NWs but it should be applicable to most types of semiconducting NWs as well. Dark field optical microscopy shows that even slight tapering of the NWs, i.e. diameter variations of a few nanometers, can be detected by a visible color change. Abrupt diameter changes of a few nanometers, as they occur for example when growth conditions vary, can be determined as well. In addition a profound analysis of the elastic scattering properties of individual GaAs NWs is presented theoretically using Mie calculations as well as experimentally by dark field microscopy. This method has the advantage that no vacuum technique is needed, a fast and reliable analysis is possible based on cheap standard hardware.

Microscopic techniques allow to investigate samples based on various contrasts such as optical, electron or magnetic. Although specialized microscopic techniques often yield convincing and sufficient information, there are many systems where just one kind of contrast does not give the whole picture and needs complementary technique. A well-known example is the combination of electron and optical microscopy especially in biological applications: Where electron microscopy gives insight into the molecular dimensions with nanometre resolution, it can not elucidate the dynamics of the biological system. This dynamic is easily visualized by optical methods, which miss the sub-wavelength resolution. The application of such two complementary methods is known as multi-modal or complementary microscopy.

The connection of biomolecules like DNA to a micro scale environment such as microarrays and Lab-on-a-chip systems is an imminent task in biochip technology. Especially in Lab-on-a-chip systems microscopic forces are used to separate the analyte from a complex mixture for further analysis [1]. In this contribution the sorting and manipulation of DNA using dielectrophoresis (DEP) on micro structured chips was investigated [2]. DEP represents an interesting approach to manipulate and control objects at the micro-[3, 4] and nanoscale range [5-7], and especially to position them at controlled locations in microelectrode arrangements. It could be shown that DNA can be reversible arranged but also permanently immobilized in micro scale electrode gaps. It was also demonstrated that it is possible to stretch and align DNA from a single molecule level to high DNA concentration in a parallel manner between microelectrodes [8]. Furthermore DNA was stretched between moveable electrodes.

DNA-based nanotechnology offers a tremendous potential for the construction and integration of defined nanoscale construct via self-assembly in building-block systems. Defined constructions from different metal nanoparticles (gold, silver and bimetallic core-shell) were demonstrated using DNA-DNA interaction. Additionally, we compared immobilization techniques for framework molecules enabling a technological implementation in a parallel way. As last step of the construction, specific metallization of DNA molecules was used for the generation of small nanowires enabling the electrical contacting to the technical periphery (electrodes).

Although functional molecular constructs promise a variety of interesting properties in combination with parallel realization and molecular precision, the utilization requires usually integration into the macroscopic world such as electrodes or other technical environments. Dielectrophoresis (DEP) represents an interesting approach to manipulate and control objects at the nanoscale, and especially to position them at controlled locations in microelectrode arrangements. Over the years this technique was established in our group and is now able to arrange either metal nanoparticles and/or DNA into these gaps in a highly reproducible manner. Microscopic tools were optimized in order to be able to follow single particles/molecules during the process. This ability greatly improves the potential, because now the key parameters can be easily tuned during live imaging of the controlled objects and their behavior. It was possible to realize bridges of nanoparticles as well as of a few stretched DNA molecules on gold microelectrode structures at chip surfaces. Moreover, DNA positioned by DEP in electrode gaps was metallized and the resulting metal nanostructure characterized. Work is in process to combine the various units as well as processes in order to access more complex functionalities.