  Ionic transport in nanopores or nanochannels is key to many cellular
processes and is now being explored as a method for DNA/polymer sequencing and
detection. Although apparently simple in its scope, the study of ionic dynamics
in confined geometries has revealed interesting new phenomena that have an
almost one-to-one correspondence with the quantum regime. The picture that
emerges is that ions can form two `quasi-particle' states, one in which they
surround themselves with other ions of opposite charge - ionic atmosphere - and
one in which semi-bound water molecules form layers at different distances from
the ions - hydration layers. The second state gives rise to two additional
effects. In the first, which is a single quasi-particle effect, the ionic
conductance through a nanopore is predicted to be `quantized' as a function of
pore radius, with the corresponding `quantization units' not related to
universal constants - like the Plank constant and the elementary charge - but
rather to the radii of the hydration layers. The second effect instead involves
the many-body interaction among ionic quasi-particles of the same sign, and
occurs when the pore has a finite capacitance to accommodate ions so that there
is a threshold concentration beyond which ions of the same sign are not
energetically allowed to enter the pore. Similar to the electron transport
case, the ionic counterpart appears only in the `quantum' regime, when the
hydration layers forming the ionic quasi-particles need to break in order to
pass through the pore. Here, we review all these phenomena, and discuss the
conditions under which they may be detected making the analogy with the
electronic transport case. Since nanopores are being considered for a host of
technological applications in DNA sequencing and detection, we expect these
phenomena will become very relevant and their understanding paramount to
progress.
