  When nanopores are used to capture and translocate DNA molecules through a
wall, the resulting capture rate is essentially independent of molecular size,
making the process incapable of changing relative concentrations in a mixture.
Using Langevin Dynamics simulations, we show that it is possible to use pulsed
fields to ratchet captured semiflexible molecules so that only short chains
successfully translocate, thus transforming translocation into a low pass
molecular filter. The process itself can be run with many pores in parallel to
increase its potential usefulness.
