We investigate the repulsive electrostatic interactions between a DNA polyelectrolyte and the charged walls of a fluidic nanoslit. The scaling of the DNA coil size with the physical slit height revealed electrostatic depletion regions that reduced the effective slit height. These regions exceeded the Debye screening length of the buffer, ${\lambda }_{\mathrm{D}}^{\mathrm{buffer}}$, and saturated at $\approx 50\mathrm{nm}$ when ${\lambda }_{\mathrm{D}}^{\mathrm{buffer}}$ reached 10 nm. We explain these results by modeling a semiflexible charged rod near a charged wall and the electrostatic screening by the polyelectrolyte. These results demonstrate the surprisingly long range over which a nanofluidic device can exert field-effect control over confined molecules.

• Received 18 September 2010

DOI:https://doi.org/10.1103/PhysRevLett.106.068302