Tuning the Migration Order in Electrokinetic Separations of <i>Saccharomyces cerevisiae</i> Cells

Traditional analytical methods such as electrophoresis and chromatography have long been employed for separating bioparticles, particularly nanosized analytes. However, the efficient separation of micrometer-sized biological particles remains a challenge. Electrokinetic (EK) systems, particularly insulator-based EK (iEK) platforms, offer promising solutions by leveraging both linear and nonlinear electrokinetic phenomena to manipulate analyte migration and separation. A key approach in analyte separations is the reversal of migration order, which has been extensively studied for small molecules but remains underexplored for biological cells. This study investigates the reversal of migration order for the separation of two strains of <i>Saccharomyces cerevisiae</i> (<i>S. cerevisiae</i>) (ATCC 9763 and ATCC 9080) cells using an iEK system under a DC voltage. A COMSOL <i>Multiphysics</i> model was employed to simulate the system and optimize the separation conditions. Then, experimental separations were conducted under both linear and nonlinear EK regimes, where the applied voltage was allowed to control the separation mechanism: size-based or charge-based. The results demonstrated that switching from a charge-based separation under a linear EK regime to a size-based separation under a nonlinear regime successfully reversed the migration order of <i>S. cerevisiae</i> cells, enhancing separation resolution. These findings highlight the potential of iEK systems for tunable separations of micrometer-sized biological analytes and provide a foundation for further applications in biological and clinical diagnostics.