Biomolecular Materials and Interfaces

Sandia National Laboratories, MS 1413

Albuquerque NM 87185-1413

We are involved in a many projects that investigate biomolecular and novel organic films. The experimental focus is developing scanning probe techniques, primarily atomic force microscopy, together with fluorescent optical probes, for understanding the nanoscale structural, mechanical, and dynamical properties of these systems. Much of our recent work has been involved in molecular-level friction and the characterization of mechanochromism in polydiacetylene mono- and tri-layers. The latter efforts are highlighted in the links below.

We also have some new programs in biomimetic systems focused on membrane structure and function. These include ligand-receptor recognition, dynamics of diffusion and organization in lipid bilayers, and translocation of biomolecules through natural and artificial pores. In addition, we are working on designing functional interfaces with molecular "motors," and interfaces for protein immobilization and transport.

Molecular spectroscopy instrumentation includes cw and femtosecond lasers, confocal imaging, and CCD detectors. These are interfaced to various scanning probe microscopes, including near-field scanning optical (NSOM), atomic force (AFM), and interfacial force (IFM). We also have a variable temperature UHV AFM and scanning tunneling microscope (STM) nearing completion.

We have discovered that both NSOM tips and AFM tips can induce a color transition in polydiacetylene thin films. By scanning the tip over the film, the molecular structure is altered, and the film transforms from a non-fluorescent state ("blue" form) to a fluorescent state ("red" form). To view movies of the transition, click the icon to the right.

Polydiacetylene films also exhibit large friction anisotropy. When the tip scans parallel to the polymer backbone direction, friction is low. Friction increases by a factor of three when the tip is scanning perpendicular to the polymer backbone direction. Click on the image to the left to see this effect exhibited in a group of domains with different backbone directions in a polydiacetylene monolayer film.

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