posted on 2016-02-19, 06:29authored byNadanai Laohakunakorn, Sandip Ghosal, Oliver Otto, Karolis Misiunas, Ulrich F. Keyser
The motion of DNA in crowded environments
is a common theme in
physics and biology. Examples include gel electrophoresis and the
self-interaction of DNA within cells and viral capsids. Here we study
the interaction of multiple DNA molecules within a nanopore by tethering
the DNA to a bead held in a laser optical trap to produce a “molecular
tug-of-war”. We measure this tether force as a function of
the number of DNA molecules in the pore and show that the force per
molecule decreases with the number of molecules. A simple scaling
argument based on a mean field theory of the hydrodynamic interactions
between multiple DNA strands explains our observations. At high salt
concentrations, when the Debye length approaches the size of the counterions,
the force per molecule becomes essentially independent of the number
of molecules. We attribute this to a sharp decrease in electroosmotic
flow which makes the hydrodynamic interactions ineffective.