Dresden 2006 – scientific programme

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CPP: Chemische Physik und Polymerphysik

CPP 26: POSTER Dynamics and Diffusion

CPP 26.9: Poster

Thursday, March 30, 2006, 17:00–19:00, P2

The flow resistance of single DNA-grafted colloids as measured by optical tweezers — •C. Gutsche¹, M. Salomo², Y.W. Kim³, R. Netz³, and F. Kremer¹ — ¹Institut für Experimentelle Physik I der Universität Leipzig — ²Institut für Biochemie der Universität Leipzig — ³Physik Department TU München

Optical tweezers are microscopic tools with extraordinary precision in the determination of the position (+/- 2 nm) of a colloid (diameter: 2.2 mum) in 3D-space and in the measurement of small forces acting on it in the range between 0.1 pN - 100 pN (pN = 10^-12 N). In rheological experiments the flow resistance of single blank or DNA-grafted colloids is determined and compared. The length of the double-stranded (ds)-DNA varies between 1000 base pairs (bp), 4000 bp and 6000 bp corresponding to contour lengths between 340 nm and 2040 nm at a grafting density of 0.03 +/- 0.01 mum^2/chain. The degree of swelling of the grafted DNA is adjusted by exchanging the ion concentration of the surrounding medium. For all examined flow velocities ranging between 100 mum/s to 1200 mum/s one observes an interesting deviation from Stokes law which can be traced back to a shear-dependent conformational change of the brush layer. The ratio of the effective hydrodynamic radii of DNA-grafted and blank colloids shows a pronounced dependence on the flow velocity, but as well on the length of the grafted DNA and the ionic strength of the solvent. The experimental findings are in qualitative agreement with hydrodynamic simulations based on an elastically-jointed chain model.