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Description
Ion-exchange membranes enable selective ion transport by allowing counterions to pass through while blocking co-ions, giving rise to ion concentration polarization (ICP) under an applied electric field. This effect creates distinct regions of ion depletion and enrichment near the membrane-electrolyte interface. At the edge of the depletion zone, where sharp conductivity gradients form, a balance between convection and electromigration facilitates the continuous concentration of dilute analytes such as bioparticles. ICP-based methods have been widely used to enhance the sensitivity of bioanalytical systems, often relying on ion-permselective membrane pairs and applied voltages to trap preconcentrated plugs [1]. However, such techniques require continuous flow and voltage to maintain the concentrated zones, complicating extraction of discrete concentrated droplets for further analysis [2]. Digital microfluidics (DMF) offers precise control of discrete droplets through patterned electrodes, enabling key operations like merging, splitting, and extraction in lab-on-a-chip devices. While efforts have been made to merge continuous and discrete microfluidics, current hybrid systems often rely on oil phases or fixed geometries that limit functionality, particularly for extracting concentrated droplets. Addressing this gap, the present study presents a hybrid platform for interfacing a continuous-flow microchannel with a DMF platform via a stagnant fluid region. This configuration enables the transfer of preconcentrated biomolecules, formed by ICP, into individually addressed droplets while maintaining their concentrated state, paving the way for efficient sample isolation and downstream processing in hybrid microfluidic systems. The experimental findings were corroborated by both simulations and analytical modeling, demonstrating qualitative consistency.
[1] S. Park, B. Sabbagh, R. Abu-Rjal, and G. Yossifon, “Digital microfluidics-like manipulation of electrokinetically preconcentrated bioparticle plugs in continuous-flow,” Lab Chip, no. 22, pp. 814–825, 2022.
[2] B. Sabbagh, S. Park, and G. Yossifon, “Enhancing commercially available immunoassays through a customized electrokinetic biomolecular preconcentration device,” Lab Chip, no. 18, pp. 4765–4775, 2025.