Counterflow gradient electrophoresis for focusing and elution

Abstract

Counterflow gradient electrofocusing uses the bulk flow of a liquid solution to counterbalance the electrophoretic migration of an analyte. When either the bulk velocity or the electrophoretic velocity of the analyte is made to vary across the length of the channel, there exists a unique zero‐velocity point for the analyte. This focusing method enables simultaneous separation and concentration of different analytes. The high resolution and sensitivity achieved are similar to that of isoelectric focusing, which separates analytes based on their isoelectric points, but the key difference is that analytes will instead focus based on their electrophoretic mobility. Dynamically changing the applied voltage or the counterflow rate over time will shift the zero‐velocity point, and therefore allows the focused analytes to pass through a fixed detection point, or elute from the separation channel. Throughout the review, a number of different counterflow gradient techniques will be discussed, along with their recent advancements and potential applications.

Investigating peak dispersion in free‐flow counterflow gradient focusing

“…The key difference is that the focal point for FF-CGF is determined by electrophoretic mobility, and this eliminates the issues associated with the pI values and carrier ampholytes. Inspired by a capillary-based equilibrium gradient method (EGM) [19,20], FF-CGF relies on applying pressure-driven flow through the chamber sidewalls to generate a velocity gradient in the transverse direction. As a result, solutes migrating laterally will focus at the point where their electrophoretic velocity is counterbalanced by the fluid flow.…”

Focusing, sorting, and separating microplastics by serial faradaic ion concentration polarization

“…Charged objects having different electrophoretic mobilities interact with EFGs in different ways. 5,6,19,[36][37][38][39] Consider, for example, EFG focusing of the two charged objects shown in Scheme 2a. 16,17,40 The interpretation of the motion of the charged objects in this illustration is essentially the same as that shown in Scheme 1a, except now there are two particles having different properties.…”

Investigating peak dispersion in free‐flow counterflow gradient focusing due to electroosmotic flow

“…As a result, solutes focus at an equilibrium position where their electrophoretic velocity is counterbalanced by the fluid flow. In principle, FF‐CGF is similar to free‐flow isoelectric focusing, except no complex buffer compositions are required, and it avoids many of the practical concerns associated with focusing a solute at its isoelectric point (p I ) [6–8].…”