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Date:  Mon, July 11, 2011
Time:  11:00 AM
Location:  Holmes Hall 389
Speaker:  Alan Hunt Department of Biomedical Engineering Center for Ultrafast Optical Science University of Michigan

Two lines of research will be presented: 1) femtosecond laser nanomachining/nanoablation and applications to biomedical research and technology, and 2) the application of optical tweezers to study the mechanics of microtubule polymerization.

Classically, the limit for optical machining is on the order of the wavelength of the incident light.  However, by taking advantage of precise, nonlinear damage mechanisms that occur for femtosecond laser pulses, damage can be achieved on a scale an order of magnitude lower, allowing precise removal of very small amounts of material mere tens of nanometers across. Femtosecond laser nanomachining can be carried out in a variety of dielectrics, and in transparent substrates machining can be sub-surface, in contrast to other nanomachining techniques such as using an electron beam or focused ion beam. We focus on the use of glass, as it is in many ways an ideal material for use in biological applications due to its chemical, optical, electrical and mechanical properties. By precisely placing laser pulses in glass, three dimensional nano and microfluidic channels and devices can be formed including nozzles, mixers, and separation columns. Recent advances allow the formation of
high aspect ratio nanochannels from single pulses, thus helping address the fabrication speed limitations presented by serial processing. These nanochannels have a range of applications including the fabrication of nanoscale pores and nanowells that may serve as vias between fluidic channels, or connecting channels to a surface. We are pursuing applications for diagnostic microfluidic devices, and basic cell biology research.

Microtubule assembly and disassembly is vital for many fundamental cellular processes, such as mitosis and cell polarization. Using a laser tweezers assay and Total Internal Reflection (TIRF) microscopy to measure in vitro microtubule assembly with nanoscale accuracy, we find fundamental inconsistencies with accepted models of this process, and as a consequence widely accepted estimates
for the kinetics are an order of magnitude too low. We find that a simple two-dimensional (2D) model predicts accurately predicts the observed behaviors, with an increasing off rate with subunit concentration due to a shift in tip structure from relatively blunt at low concentrations to relatively tapered at high concentrations. These findings have major implications for understanding how microtubules are regulated, and the actions of important drugs that target microtubules, such as taxol, vinca alkaloids, epithilones and colchicine, which are widely used for chemotherapy, treatment of gout, and drug-coated stents.