Dresden 2006 – wissenschaftliches Programm

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CPP: Chemische Physik und Polymerphysik

CPP 4: New Experimental Techniques

CPP 4.1: Hauptvortrag

Montag, 27. März 2006, 14:00–14:30, ZEU Lich

Optical tweezers - novel tools in nanophysics — •Friedrich Kremer, Christof Gutsche, Kati Kegler, Mathias Salomo, Joerg Reinmuth, and Wiktor Skokow — University of Leipzig, Institute of Experimental Physics I

Optical tweezers are microscopic tools with extraordinary resolution.(resolution in space: ± 1 nm, resolution in force: ± 50 fN) In the talk three different experiments will be discussed: 1.) Measurement of the force-extension dependence of single chains of double stranded DNA having a length between 1000 base pairs (bp) to 6000 bp. It is shown that the wormlike chain model fits the data. 2.) Measurement of forces of interaction between single blank and DNA-grafted colloids. The forces are measured in two directions, parallel and perpendicular to the axis between the two colloids under study. Bringing the DNA-grafted colloids in close contact (< 100 nm for 4000 bp DNA) enables one to measure directly the forces necessary to interdigitate the DNA-brushes. Under these conditions frictional stick-slip phenomena take place, when the colloids are moved perpendicularly to its central axis. 3.) Measurement of the flow resistance of single colloids grafted with DNA of lengths between 1000 bp to 6000 bp. The experiments can be described by Stokes law with an effective hydrodynamic radius being dependent on the flow velocity, the length, the grafting-density and the ionic strength of the surrounding medium.