Dresden 2006 – wissenschaftliches Programm
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CPP: Chemische Physik und Polymerphysik
CPP 4: New Experimental Techniques
CPP 4.13: Vortrag
Montag, 27. März 2006, 17:30–17:45, ZEU Lich
Blowing DNA bubbles — •Nikolai Severin1, Wei Zhuang1, Christof Ecker1, Alexei A. Kalachev2, Igor M. Sokolov1, and Jürgen P. Rabe1 — 1Department of Physics, Humboldt University Berlin, Newtonstr. 15, D-12489 Berlin, Germany — 2Plasmachem GmbH, Rudower Chaussee 29, D-12489 Berlin, Germany
Liquids at the interface with a solid differ from their bulk state since they order in molecular layers parallel to the substrate surface. With a surface forces apparatus, the layers can be squeezed out one by one at increasing normal forces, indicating solid-like behavior in the direction normal to the substrate. Similar layered behavior is observed for free liquid thin films on a surface. Computer simulations, measurements of shear forces and tracer dye diffusion, however, indicate liquid-like behavior parallel to the substrate. Therefore, we regard an ultra-thin layer of a liquid on a solid substrate as a quasi 2D-liquid. Here we demonstrate that such a layer may be used to transmit forces isotropically across a surface. A scanning force microscope (SFM) tip was employed to generate a 2D-pressure, which then exerts a force on a single macromolecule embedded in the 2D-liquid. In particular, supercoiled ds-DNA has been unraveled, moved, stretched, overstretched to 2.0 times its B-form length and then torn apart at (1.1 +/- 0.2) nN.