Electroosmotic flow and DNA electrophoretic transport in micro/nano channels.

摘要

In Micro/nano fluidic systems, electrokinetic transport is a convenient method to move materials, such as water, ions and particles for fast, high-resolution and low-cost analysis and synthesis. It has wide applications to drug delivery and its control, DNA and biomolecular sensing, manipulation, the manufacture laboratories on a microchip (lab-on-a-chip) and many other areas. In the present work, electrokinetically driven fluid flow and particle transport in micro/nanoscale channels/pores with heterogeneous surface potential or converging shape are investigated theoretically and numerically.;A step change in wall potential is found to induce a recirculation region in the bulk electroosmotic flow and interesting flow structures can be achieved by manipulating the surface heterogeneous patterns. Most of the previous work on this problem is based on the Debye-Huckel approximation and the validity of Boltzmann distribution for ionic species. In the present work, ionic species distributions in the electric double layers are found to be different from the Boltzmann distribution and this deviation is more noticeable for higher applied electric field.;A mathematical model is developed to simulate the electroosmotic flow (EOF) and the transport of embedded particles in micro/nano nozzles/diffusers. Results can be used to estimate the mass transport of charged/uncharged species in micro/nano nozzles/diffusers which has a potential application in transdermal drug delivery. The model is extended to investigate the DNA electrophoretic transport through a converging nanopore for the purpose of DNA sequencing. The flow field, the resistive forces acting on the DNA, the DNA velocity and the ionic current through the nanopore are calculated numerically based on the Poisson-Boltzmann theory and the lubrication approximation. It is found that the electroosmotic flow inside the nanopore plays an important role in the DNA translocation process and the resulting viscous drag decreases the effective driving force acting on the DNA substantially. Entropic forces, used to be considered as the main resistive forces in previous works, are found to be small and negligible. Modeling and simulations are validated by the good agreement with the experimental data for the tethering force and the DNA velocity.