  We present a new concept for the separation of DNA molecules by contour
length that combines a nanofluidic ratchet, nanopore translocation and pulsed
fields. Using Langevin Dynamics simulations, we show that it is possible to
design pulsed field sequences to ratchet captured semiflexible molecules in
such a way that only short chains successfully translocate, effectively
transforming the nanopore process into a low pass molecular filter. We also
show that asymmetric pulses can significantly enhance the device efficiency.
The process itself can be performed with many pores in parallel, and it should
be possible to integrate it directly into nanopore sequencing devices,
increasing its potential utility.
