Abstract
Dielectrophoresis (DEP) is a versatile technique for the solution of difficult (bio-)particle separation tasks based on size and material. Particle motion by DEP requires a highly inhomogeneous electric field. Thus, the throughput of classical DEP devices is limited by restrictions on the channel size to achieve large enough gradients. Here, we investigate dielectrophoretic filtration, in which channel size and separation performance are decoupled because particles are trapped at induced field maxima in a porous separation matrix. By simulating microfluidic model porous media, we derive design rules for DEP filters and verify them using model particles (polystyrene) and biological cells (S. cerevisiae, yeast). Further, we bridge the throughput gap by separating yeast in an alumina sponge and show that the design rules are equally applicable in real porous media at high throughput. While maintaining almost 100% efficiency, we process up to 9 mL min−1, several orders of magnitude more than most state-of-the-art DEP applications. Our microfluidic approach provides new insight into trapping dynamics in porous media, which even can be applied in real sponges. These results pave the way toward high-throughput retention, which is capable of solving existing problems such as cell separation in liquid biopsy or precious metal recovery.
Highlights
Separation of micron and sub-micron particles from liquid or according to their properties is a highly relevant topic in a variety of fields, for example, in pharmaceutical production[1,2], in diagnostics and analytics[3], or in the recovery of materials[4,5]
If the particle is less polarizable than the surrounding medium, it moves towards regions of low field, which is termed negative DEP
The dependence of Re[K] on the particle properties explains the versatility of DEP: It is possible to solve difficult separation tasks since particles of equal size and density could be moved into different directions in the electric field due to different polarizabilities
Summary
Separation of micron and sub-micron particles from liquid or according to their properties is a highly relevant topic in a variety of fields, for example, in pharmaceutical production[1,2], in diagnostics and analytics[3], or in the recovery of materials[4,5]. The real part of the Clausius-Mossotti function gives the relative polarizability of the particle in the medium It is dependent on the permittivities and conductivities of the medium and the particle as well as on the frequency of the applied ac field. If the particle is less polarizable than the surrounding medium, it moves towards regions of low field (against the gradient), which is termed negative DEP (nDEP). If the particle is better polarizable than the medium it moves in direction of the gradient towards regions of highest field strength, termed positive DEP (pDEP). The dependence of Re[K] on the particle properties explains the versatility of DEP: It is possible to solve difficult separation tasks since particles of equal size and density could be moved into different directions in the electric field due to different polarizabilities
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