Unraveling Enrichment Mechanism of Paper-Based Concentrator Based on Ion Concentration Polarization: Modeling and Experiment

Paper-based concentrators based on ion concentration polarization (ICP) have exhibited significant potential for trace molecular enrichment, but the underlying enrichment mechanism remains unclear. We established a numerical model with experimental validation to investigate the particle mass transfer behavior under the ICP effect in paper-like porous media. The results reveal that the preconcentration of charged particles on the paper-based platform results from the synergistic effects of electroosmotic flow (EOF), electrophoresis (EP), and capillary force (<b>F</b>_C). Due to the porous nature of the paper-based platform, significant hydraulic and electrical resistances are generated, which hinder the formation of secondary EOF. Compared with the conventional ICP effect observed in microfluidic channels, the achievable enrichment factor is much lower than that in microfluidic systems. Specifically, since the applied voltage is positively correlated with both electrophoretic and electroosmotic velocities while the <b>F</b>_C remains constant, the original force balance is disrupted once the voltage exceeds a certain threshold, resulting in a two-stage variation in the enrichment factor. When the ratio of the initial analyte concentration to the buffer concentration was 0.07, optimal enrichment was achieved, yielding an enrichment factor of more than 13 times. This is attributed to the ion concentration and the complete formation of the depletion zone. These findings were subsequently validated through experiments, showing strong agreement with numerical simulation results. This study provides a theoretical basis and predictive model for a paper-based concentrator, which offers important implications for its applications in biological, chemical, and environmental sciences.