This thesis is about growth of Au-assisted and self-assisted InAs nanowires (NWs). The wires are synthesized using a solid source molecular beam epitaxy (MBE) system and characterized with several techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM) and x-ray diffraction. InAs NWs can be used in a broad range of applications, including detectors, high speed electronics and low temperature transport measurements, but in this thesis focus will be put on biological experiments on living cells.

Good control of Au-assisted InAs NW growth has been achieved by a systematic study to optimize the growth conditions; first the Au deposition, then the growth temperature and finally the beam fluxes. For further control of the growth, Au droplets have been positioned with electron beam lithography and large scale arrays with a > 99 % yield have been made on 2 inch substrates. The crystal structure of the NWs has also been investigated, and a method for obtaining pure wurtzite NWs with a well controlled diameter and length is presented.

For self-assisted growth of InAs NWs a method for enhanced control of the nanowire morphology by pre-treatment of the oxide layer is presented. A series of experiments with formation of a droplet on top of the wires has been carried out and pyramidal shaped structures at the NW top with pure zinc blende crystal structure are observed.

A novel in-situ experiment with fabrication of NWs and simultanous characterization using x-ray diffraction is performed with a MBE system attached to a synchrotron beam line. The evolution in crystal structure is monitored for different growth conditions and can be correlated to post growth analysis in TEM. This type of studies gives much more detailed information on formation of the crystal structure and its dependence on growth parameters.

By fabricating the NWs on silicon-on-insulator substrates we demonstrate electrically addressable NWs that are still standing vertically on the substrate and can potentially be used for intra-cellular recordings. Devices for biological experiments using vertically aligned carbon nanofibers have also been fabricated and some of these experiments are described here. By virtually stabbing the nanostructures into living cells, we report a method for fast delivery of plasmid, which can be observed with fluorescence microscopy.

Also, devices for capture of circulating tumor cells (CTCs) have been fabricated. The CTC concentration is extremely low and highly effective devices for capturing the CTCs may improve the treatment of cancer patients.