  Tunable nanopores in elastomeric membranes have been used to study the
dependence of ionic current blockade rate on the concentration and
electrophoretic mobility of particles in aqueous suspensions. A range of
nanoparticle sizes, materials and surface functionalities has been tested.
Using pressure-driven flow through a pore, the blockade rate for 100 nm
carboxylated polystyrene particles was found to be linearly proportional to
both transmembrane pressure (controlled between 0 and 1.8 kPa) and particle
concentration (between 7 x 10^8 and 4.5 x 10^10 mL^-1). This result can be
accurately modelled using Nernst-Planck transport theory. Using only an applied
potential across a pore, the blockade rates for carboxylic acid and amine
coated 500 nm and 200 nm silica particles were found to correspond to changes
in their mobility as a function of the solution pH. Scanning electron
microscopy and confocal microscopy have been used to visualise changes in the
tunable nanopore geometry in three dimensions as a function of applied
mechanical strain. The pores observed were conical in shape, and changes in
pore size were consistent with ionic current measurements. A zone of inelastic
deformation adjacent to the pore has been identified as critical in the tuning
process.
