Paul Hansma's group continues their work in finding the fundamental limits on the performance of Atomic Force Microscopes (AFMs), and then building AFMs that come closer to those fundamental limits. These new microscopes are applicable to problems of fundamental and practical interest in materials research, biology, and biomineralization, just to name a few fields. Specifically, Paul's group works toward the development of AFMs for small cantilevers, which allow faster and more gentle imaging of biological systems.

Electron Micrographs of two different AFM cantilever tips, each with a nontube attached.

With the advent of these small cantilever microscopes, we can begin to analyze biological processes such as enzyme activation (e.g. transcription, protein folding) in real time at single molecule resolution.

In collaboration with Profs. Dan Morse and Galen Stucky (Chemistry) we have elucidated one of nature's secrets in making strong and tough natural fibers such as the organic material found in abalone shells. Recently, published in the journal Nature (399: 761, 1999), they show polymers found in the abalone shell possess a modular structure.

Scanning and transmission electron micrographs of a freshly cleaved abalone shell, showing adhesive ligaments formed between nacre tablets.

They proposed that this modular structure possesses intermediate strength bonds that allow the subunit of the molecule to elongate in a stepwise manner as folded domains or loops are pulled open.

Model of long polymers and force-extension curves for different kinds of polymers.

The elongation events occur forces much smaller than the forces required to break the backbone of the molecule. We believe that this 'modular' elongation mechanism might prove to be quite general for conveying toughness to natural fibers and adhesives.