An electrokinetic preconcentration trapping pattern in electromembrane microfluidics

Abstract

Electrokinetic flows near ion-selective membranes, which produce field amplification and electrokinetic preconcentration, have broad applications in preconcentration engineering since almost all electrochemical chips live in saline surroundings. Despite some published work related to electrokinetic molecular concentration, the electrokinetic trapping pattern has not yet been investigated in previous experimental and theoretical studies. By finite element simulations, the paper is concerned with the transition behavior of the trapping pattern in a membrane-embedded microfluidic channel. Regulating the cross-membrane voltage, Debye number, and surface charge, the local interaction of electric field force and electro-osmotic flow distorts the trapping location, resulting in the realization of a series of trapping patterns switches. We find the transition behavior of the trapping pattern in a membrane-embedded microfluidic channel, from a plateau preconcentration plug outside the vortex to a plug with a Gaussian-like distribution and even to a final spike-like pattern of stagnation points inside the vortex. For a small Debye number, the trapping patterns are characterized by stagnation points, an electrokinetic preconcentration pattern formed inside the vortex, and a concentration with spike-like shapes. Upon increasing the cross-membrane voltage and surface charge, the effect of local vortices can modulate the scaling behavior of enrichment factors at the stagnation points, yet the platform preconcentration plug is basically consistent with the existing experimental observations. These intriguing phenomenological patterns have promising applications in separation, desalination, and electrochemistry.