Predicting ion concentration polarization and analyte stacking/focusing at nanofluidic interfaces

Abstract

We report on the investigation of electropreconcentration phenomena in micro/nanofluidic devices integrating 100-µm-long nanochannels using 2D COMSOL simulations based on the coupled Poisson-Nernst-Planck and Navier-Stokes system of equations. Our numerical model is used to demonstrate the influence of key governing parameters such as electrolyte concentration, surface charge density, and applied axial electric field on ion concentration polarization (ICP) dynamics in our system. Under sufficiently extreme surfacecharge-governed transport conditions, ICP propagation is shown to enable various transient and stationary stacking and counter-flow gradient focusing mechanisms of anionic analytes. We resolve these spatiotemporal dynamics of analyte and electrolyte ICP over disparate time and length scales, and confirm previous findings that the greatest enhancement is observed when a system is tuned for analyte focusing at the charge-excluding microchannel-nanochannel electrical double layer (EDL) interface. Moreover, we demonstrate that such tuning can readily be achieved by including additional nanochannels oriented parallel to the electric field between two microchannels, effectively increasing the overall perm-selectivity and leading to enhanced focusing at the EDL interfaces. This approach shows promise in providing added control over the extent of ICP in electrokinetic systems, particularly under circumstances in which relatively weak ICP effects are observed using only a single channel.

Analyte Enrichment via Ion Concentration Polarization with Hydrogel Plugs Polymerized in PDMS Microchannels by a Facile and Comprehensive Method for Improved Polymerization

“…The 5% IRG hydrogel enriched Alexa Fluor 488 by ∼80-fold, while 0.2% VA-086 hydrogel enriched it by ∼120-fold in 5 min, which is near the enrichment shock stack theoretical limit of 100×. 18 The enrichment ability relates to the properties of the ionpermselective element (hydrogel), including the surface charge density, the number of nanochannels, 49 and water permeability. 50 The performance difference between IRG and VA-086 hydrogel supports the hypothesis that even with the same monomer compositions, the micro/nanostructures are different.…”