Electrokinetic transport phenomena in nanofluidic devices

Nanofluidic devices have wide potential applications in biology, chemistry and medicine, and have been proven to be very valuable in sensing biological particles (e.g., DNA and proteins) due to their efficiency, sensitivity and portability. Electrokinetic control of ion, fluid, and particle transport by using only electric field is the most popular method employed in nanofluidic devices. A comprehensive understanding of the electrokinetic ion, fluid, and particle transport in nanofluidics is essential for developing nanofluidic devices for the detection of single molecules, such as the next generation nanopore-based DNA sequencing technology. This research explored numerical simulation of electrokinetic ion and fluid transport in both solid-state and soft nanopores, and also explored the electric field induced translocation of nanoparticles through solid-state and soft nanopores using a continuum based model.;In the first part of this dissertation, electrokinetic ion and fluid transport in two types of nanopores, charge-regulated solid-state and polyelectrolyte (PE)-modified soft nanopores, have been investigated for the first time using a continuum-based model, composed of the coupled Poisson-Nernst-Planck (PNP) equations for the ionic mass transport, and Stokes and Brinkman equations for the flow fields. Concentration polarization phenomenon, ionic conductance, potential drop inside the nanopore, and flow field as functions of the solution properties including pH and ionic strength, charge properties of the nanopore, properties of the soft layer, and the electric field strength imposed were investigated. The results show that the electrokinetic ion and fluid transport in nanopore-based devices can be regulated by tuning pH and/or ionic strength and the properties of the polyelectrolyte layer grafted on the membrane wall. One could use the induced concentration polarization phenomenon to reduce the electric field inside the nanopore for slowing down nanoparticle translocation through the nanopore.;One major challenge in the nanopore-based DNA sequencing technology is to slow down DNA translocation for improving the read-out accuracy. Therefore, the second part of this thesis focused on numerical investigations of nanoparticle translocation through a nanopore. Three types of nanoparticles, which include soft nanoparticle consisting of a rigid core covered by a soft layer, DNA, and charge-regulated soft nanoparticle such as protein, in both solid-state and soft nanopores were considered. Based on the results, regulating DNA translocation by using the soft nanopore was proposed to simultaneously enhance the nanopore capture rate and slow down DNA translocation inside the nanopore. Versatile manipulations of charge-regulated nanoparticles, including separation, focusing, trapping and pro-concentration by using soft nanopores can be achieved by adjusting pH, background salt concentration, and the properties of the soft layer grafted on the nanopore wall. Regulation of DNA translocation by using a solid-state nanopore with a floating electrode coated on the inner surface of the nanopore was also proposed and investigated using numerical simulation.