  A polymer chain confined in nano-scale geometry has been used to investigate
the underlying mechanism of Nuclear Pore Complex (NPC), where transport of
cargoes is directional. It was shown here that depending on the solvent quality
(good or poor) across the channel, a polymer chain can be either inside or
outside the channel or both. Exact results based on the short chain revealed
that a slight variation in the solvent quality can drag polymer chain inside
the pore and {\it vice versa} similar to one seen in NPC. Furthermore, we also
report the absence of crystalline (highly dense) state when the pore-size is
less than the certain value, which may have potential application in packaging
of DNA inside the preformed viral proheads.
