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

TL;DR

This study presents a comprehensive numerical analysis of particle preconcentration in micro-channels with permselective membranes, revealing key mechanisms and conditions affecting particle enrichment for device optimization.

Contribution

It introduces a detailed multi-physics simulation approach that captures complex ion and particle dynamics without simplifying assumptions, advancing understanding of electrokinetic preconcentration.

Findings

Electroosmotic flow and electrophoretic force interplay determines particle trapping.

Ion concentration and particle enrichment depend on voltage, initial concentration, and buffer composition.

Validity conditions for decoupled models are established based on charge ratios.

Abstract

This paper studies mechanism of preconcentration of charged particles in a straight micro-channel embedded with permselective membranes, by numerically solving 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 trough 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 may 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 a condition for validity of decoupled simulation model is given based on charges carried by focused charge particles and that by buffer co-ions. These results provide important guidance in the design and optimization of nanofluidic preconcentration and other related devices.