The nanofluidic diode, as one of
the emerging nanofluidic logic
devices, has been used in many fields such as biosensors, energy harvesting,
and so on. However, the entrance effects of the nanofluidic ionic
conductance were less discussed, which can be a crucial factor for
the ionic conduction. Here we calculate the ionic conductance as a
function of the length-to-pore ratio (<i>L</i>/<i>r</i>), which has a clear boundary between nanopore (surface dominated)
and nanochannel (geometry dominated) electrically in diluted salt
solution. These entrance effects are even more obvious in the rectified
ionic conduction with oppositely charged exterior surfaces of a nanopore.
We build three modelsExterior Charged Surface model (ECS),
Inner Charged Surface model (ICS), and All Charged Surface model (ACS)to
discuss the entrance effects on the ionic conduction. Our results
demonstrate, for a thin nanopore, that the ECS model has a larger
ionic rectification factor (<i>Q</i>) than that of ICS model,
with a totally reversed tendency of <i>Q</i> compared to
the ICS and ACS models as <i>L</i>/<i>r</i> increases.
Our models predict an alternative option of building nanofluidic biosensors
that only need to modify the exterior surface of a nanopore, avoiding
the slow diffusion of molecules in the nanochannel
