Ionic channels are bioselective pipes that can have exquisite selectivity for a particular chemical species, e.g., for a pathogenic chemical. These charge densities are many orders of magnitude higher than the fixed charge densities of semiconductors, because the pore of the channel is so small. Many channels are supposed to have of the order of 6 formal charges in their selectivity filter. Selectivity is not enough. If channels just bound chemicals selectivity they would be of limited use, because the chemicals would not move.
Channels have the other most useful feature that they allow large fluxes of what they select.
Channels achieve this combination of high permeability and high selectivity by cramming a large amount of fixed charge into a very small region. We propose to do just the same to make channels selective for pathogens and to allow enough flux for the pathogens to flow through in large amounts, and thus to clear them from the environment. This is our long term goal. In the short term, we must understand channels, prove that our understanding is correct, and convince enough of our colleagues, so our entire community will make the pathogen sensitive channels we need. They key to using ionic channels in this way is to understand the basis of selectivity so we can control it.