  Control and transport of nanoscale objects in fluids is challenging because
of the unfavorable scaling of most interaction mechanisms to small length
scales. We design energy landscapes for nanoparticles by accurately shaping the
geometry of a nanofluidic slit and exploiting the electrostatic interaction
between like charged particles and walls. Directed transport is performed by
combining asymmetric potentials with an oscillating electric field to achieve a
rocking Brownian motor. Using 60\,nm diameter gold spheres, we investigate the
physics of the motors with high spatio-temporal resolution, enabling a
parameter-free comparison with theory. We fabricated a sorting device that
separates 60- and 100-nanometer particles in opposing directions within
seconds. Modeling suggests that the device separates particles with a radial
difference of 1 nanometer.
