High-throughput dielectrophoretic filtration of sub-micron and micro particles in macroscopic porous materials

Abstract

State-of-the-art dielectrophoretic (DEP) separation techniques provide unique properties to separate particles from a liquid or particles with different properties such as material or morphology from each other. Such separators do not operate at throughput that is sufficient for a vast fraction of separation tasks. This limitation exists because high electric field gradients are required to drive the separation which are generated by electrode microstructures that limit the maximum channel size. Here, we investigate DEP filtration, a technique that uses open porous microstructures instead of microfluidic devices to easily increase the filter cross section and, therefore, also the processable throughput by several orders of magnitude. Previously, we used simple microfluidic porous structures to derive design rules predicting the influence of key parameters on DEP filtration in real complex porous filters. Here, we study in depth DEP filtration in microporous ceramics and underpin the previously postulated dependencies by a broad parameter study (Lorenz et al., 2019). We will further verify our previous claim that the main separation mechanism is indeed positive DEP trapping by showing that we can switch from positive to negative DEP trapping when we increase the electric conductivity of the suspension. Two clearly separated trapping mechanisms (positive and negative DEP trapping) at different conductivities can be observed, and the transition between them matches theoretical predictions. This lays the foundation for selective particle trapping, and the results are a major step towards DEP filtration at high throughput to solve existing separation problems such as scrap recovery or cell separation in liquid biopsy.

Dielectrophoresis: Developments and applications from 2010 to 2020

“…Lorenz et al. describes a new type of particle separation technique that involves DEP‐enhanced filtration allowing for the retention and release of sub‐micron particles [110]. Here, they used open porous microstructures consisting of ceramic filters/glass beads as a filter material sandwiched between electrodes.…”

A review of dielectrophoretic separation and classification of non‐biological particles

“…Naturally, aqueous media are preferred in many applications due to a higher flexibility. A possible bridge over the throughput gap might lie in aqueous DEP filters [81] which give promising results for selective particle capture at high throughput. The high selectivity and controllability of DEP filtration could allow more flexible applications compared to conventional industrial separation methods.…”

“…We further employed monolithic mullite foams with median pore window diameters from 180 to 270 µm ( Fig. 6B and D), and demonstrated that DEP filtration can effectively separate polystyrene and graphite particles of different sizes (0.5, 3, and 4.5 µm) from aqueous medium at high volumetric flow rates from 1 to 9 mL/min [81]. Applying 600 V rms at 15 kHz, we achieved separation efficiencies between 60 and 100% depending on throughput for 500 nm polystyrene particles.…”

“…Ideally, the pore size is much larger than the target particle size so that separation is (almost) independent of mechanical filtration and dominated by the DEP force. The macroscopic porous medium can be monolithic or a packed bed and is either sandwiched between two electrodes [80][81][82][83][84][85] or arranged between two [86][87][88] or more [89] concentric electrodes. Electric field maxima are on the surface of the pores or at contact points of the packing material forming the porous medium ( Fig.…”

“…6C). Further, we could resuspend 92% of formerly trapped particles by increasing the flow rate and turning off the electric field [81].…”