Accurate Multi-Physics Numerical Analysis of Particle Preconcentration Based on Ion Concentration Polarization

This paper studies the mechanism of preconcentration of charged particles in a straight microchannel embedded with permselective membranes by numerically solving the coupled transport equations of ions, charged particles and solvent fluid without any simplifying assumptions. It is demonstrated that trapping and preconcentration of charged particles are determined by the interplay between drag force from the electroosmotic fluid flow and the electrophoretic force applied through the electric field. Several insightful characteristics are revealed, including the diverse dynamics of co-ions and counter ions, replacement of co-ions by focused particles, lowered ion concentrations in particle-enriched zone, and enhanced electroosmotic pumping effect, etc. Conditions for particles that can be concentrated are identified in terms of charges, sizes and electrophoretic mobilities of particles and co-ions. Dependences of enrichment factor on cross-membrane voltage, initial particle concentration and buffer ion concentrations are analyzed and the underlying reasons are elaborated. Finally, post priori condition for the validity of decoupled simulation model is given based on the charges carried by focused particles and buffer co-ions. These results provide an important guidance in the design and optimization of nanofluidic preconcentration and other related devices.