  Recent experiments of translocation of double stranded DNA through nanopores
[M. Wanunu \textit{et al.} Nature Nanotech. {\bf 5}, 160 (2010)] reveal that
the DNA capture rate can be significantly influenced by a salt gradient across
the pore. We show that osmotic flow combined with electrophoretic effects can
quantitatively explain the experimental data on the salt-gradient dependence of
the capture rate.
