Fabrication and mechanical characterization of novel nanometer scale devices for application in life sciences and engineering has been realized. Two nanodevices were developed and tested during the course of this study: one is a prototype microtome knife for sectioning biological materials, made by welding a multiwall nanotube across the gap between two sharpened tungsten needles. The other is a nanotube/sphere device for use as a nanonewton force sensor. Both devices were fabricated using a piezoelectric-based 3-D manipulator under direct view in a scanning electron microscope (SEM).

Mechanical characterization of the prototype microtome knife was done by performing load tests using an atomic force microscope (AFM) cantilever inside a SEM. Initial tests indicated a maximum breaking force of 1.4 μN. In situ cutting experiments on epon resin (biological cell embedding material) have revealed indentations made by pressure from nanotube in the microtome knife. In an effort to obtain a thinner nano-knife, an individual free standing nanotube was exposed to the 248 nm beam from a KrF excimer laser. The laser treatment resulted in selective exfoliation of amorphous contamination layer surrounding the multiwalled carbon nanotube (MWCNT). The results were confirmed by comparing transmission electron microscopy (TEM) images of the nanotube before and after the exposure.

The nanotube/sphere device consists of a polystyrene microsphere (4-15 μm in diameter) attached to a MWCNT (5-50 μm long) whose other end is attached to a microscopy probe. The force vs. deflection behavior of this device was calibrated for varying nanotube dimensions. Calibration curves indicate forces in the range of (10^-8 to 10^-9) N for nantube length in the range (8 to 15) μm. The device will be used for studying deformation behavior of sensory hair bundles. The bending modulus calculated from calibration tests for individual nanotubes ranged 11-59 GPa, these values agree with values available in literature. Two more potential applications of this device were explored. One is the laser trapping of a microsphere in air for nanotube lengths > 15 μm. For this, a sphere attached to a nanotube was optically trapped by use of a 1064 nm laser at 100 mW average power. The maximum measured sphere deflection was approximately 3 μm. The second application is in bio-optics for emulating a cell nucleus. In this case a 13.1 μm diameter sphere was modeled as a Mie scatterer, and its scattering spectrum was compared with the experimental data. The data obtained will help in understanding the scattering behavior of actual biological cells, as well as in the development of a more complicated tissue phantom required for volumetric sampling using the optical coherence tomography (OCT) system.

In addition to the work with carbon nanotubes, the SEM based manipulation system was also used for demonstrating 3-D manipulation of individual semiconducting GaN nanowires. A specimen comprised of an individual, freestanding GaN nanowire was also prepared for atom probe tomography of the nanowire.