Dresden 2006 – scientific programme

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AKB: Biologische Physik

AKB 18: Ion Channels and Nanopores

AKB 18.3: Talk

Wednesday, March 29, 2006, 16:15–16:30, ZEU 255

Direct force measurements on DNA in a solid-state nanopore — •U. F. Keyser, B. N. Koeleman, D. Krapf, R. M. M. Smeets, S. G. Lemay, N. H. Dekker, and C. Dekker — Kavli Institute of Nanoscience, Delft University of Technology, The Netherlands

Amongst the variety of roles for nanopores in biology, an important one is enabling polymer transport, for example in gene transfer between bacteria and transport of RNA through the nuclear membrane. Recently, this has inspired the use of protein and solid-state nanopores as single-molecule sensors for the detection and structural analysis of DNA and RNA by voltage-driven translocation. The magnitude of the force involved is of fundamental importance in understanding and exploiting this translocation mechanism, yet so far has remained unknown. Here, we demonstrate the first measurements of the force on a single DNA molecule in a solid-state nanopore by combining optical tweezers with ionic current detection. The opposing force exerted by the optical tweezers can be used to slow down and even arrest the translocation of the DNA molecules. We obtain a value of 0.24*0.02 pN/mV for the force on a single DNA molecule, independent of salt concentration. Our data allow the first direct quantitative determination of its effective charge of 0.53*0.05 electrons per base pair, corresponding to a 73% reduction of the bare DNA charge. Our novel single-molecule technique further is a major step forward in biotechnology (towards rapid DNA sequencing) and biophysics (study of unfolding of RNA or DNA-protein binding).