The nonlinear electromigration of analytes into confined spaces

TL;DR

This paper investigates the nonlinear behavior of analyte electromigration into confined microfluidic channels, revealing how nonlinear ionic interactions affect the concentration and injection efficiency of samples.

Contribution

A reduced nonlinear model for analyte electromigration in confined spaces is derived and numerically analyzed, highlighting the impact of nonlinear ionic coupling on injection efficiency.

Findings

Injected sample concentration can be significantly lower than reservoir concentration.

Nonlinear ionic interactions influence the shape and mass of the propagating wave.

The model predicts how injection depends on initial sample concentration.

Abstract

We consider the problem of electromigration of a sample ion (analyte) within a uniform background electrolyte when the confining channel undergoes a sudden contraction. One example of such a situation arises in microfluidics in the electrokinetic injection of the analyte into a micro-capillary from a reservoir of much larger size. Here the sample concentration propagates as a wave driven by the electric field. The dynamics is governed by the Nerst-Planck-Poisson system of equations for ionic transport.A reduced one dimensional nonlinear equation describing the evolution of the sample concentration is derived.We integrate this equation numerically to obtain the evolution of the wave shape and determine how the the injected mass depends on the sample concentration in the reservoir.It is shown that due to the nonlinear coupling of the ionic concentrations and the electric field, the concentration of the injected sample could be substantially less than the concentration of the sample in the reservoir.