In addition to its annual lectures, ChBE hosts a weekly seminar throughout the year with invited lecturers who are prominent in their fields. This seminar will take place in the Parker H. Petit Biotechnology Building (IBB), Room 1128, from 3-4 p.m. on Monday, Jan. 13. Refreshments are served at 2:30 p.m.

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Hitching a ride at the nanometer scale: passive and active transport in complex media

Transport in crowded and complex media is a ubiquitous problem both in technology and biology in processes as diverse and far apart as flow of emulsions in nanoporous rocks and vesicle transport in biological cells. On a molecular scale, transport can be diffusive or driven. In this talk, I will introduce single-walled carbon nanotubes (SWNTs) as highly versatile multi-scale probes to investigate different modes of transport in media of increasing complexity. Using SWNTs as the ideal stiff filament, I will discuss the confined dynamics of stiff macromolecules in crowded environments, a common feature of polymer composites and the cell cytoskeleton. In fixed porous networks, SWNTs reptate in the network and rotational diffusion constant is proportional to the filament bending compliance and counter-intuitively, independent of the network porosity. In equilibrium and non-equilibrium biopolymer networks, the dynamics of SWNTs is more complex. I will discuss a newly developed microrheology technique in which we use nanotubes as “stealth probes” to measure viscoelastic properties of the host media. Finally I will present a quantitative study of the motions of molecular targets tagged with SWNTs in cells and whole organisms over times from ms to hours. In addition to thermal diffusion and directed motor protein transport, we document a new regime of active random “stirring” which may drive an intermediate mode of transport. The random stirring by the cytoskeleton should cause active diffusion in the narrow confines of the cell periphery leading to enhanced, non-specific transport. I will present a quantitative model connecting molecular mechanisms to these mesoscopic fluctuations.