Free Solution Microfluidic Separations of Particles and Cells with Nonlinear Electrophoresis

Abstract Insulator-based electrokinetic (iEK) platforms integrate insulating structures within microchannels to amplify nonlinear electrophoresis (EPNL) effects and improve separation efficiency, as such effects scale with the electric field magnitude and introduce more discriminatory characteristics. In contrast, free solution platforms, used in conventional capillary electrophoresis (CE) systems, traditionally neglect EPNL effects and rely on the electrical charge of target analytes alone to perform separations by employing linear electrophoresis (EPL). In this work, the effects of EPNL in free solution platforms are tested by separating a binary mixture of microparticles and a charge-identical binary mixture of microparticles and Bacillus cereus cells. While analytical techniques typically face a trade-off between being ″good″ (high resolution) or ″fast″ (short duration), the results show that EPNL can be exploited to deliver on both aspects simultaneously. Using EPNL increased separation resolution (Rs) by up to 50% and decreased separation duration by 56%, making separations with EPNL both faster and better compared to platforms relying on EPL alone. Furthermore, separations of a binary mixture of microparticles and cells achieved resolution values >2.0 when EPNL effects were accentuated, well above the gold standard of 1.5. To the best of our knowledge, this work represents the first of its kind where such a comprehensive advantage of EPNL in free solution is reported, effectively overcoming the traditional performance trade-offs of open channel electrokinetic separations.