Gabriele Gradl

Paired microelectrode system: dielectrophoretic particle sorting and force calibration

Abstract We describe a closed microsystem used for free-flow dielectrophoretic separation of particles and cells. Particles have been separated on the basis of size and cells separated from artificial particles. Dielectrophoretic forces were calculated numerically and compared with experimental and analytic results. While the influence of local heating is of minor importance under our experimental conditions, the consideration of liquid-channel interfaces gives rise to an remarkable increase of dielectrophoretic forces.

The potential of dielectrophoresis for single-cell experiments

In this article, a microfluidic system was developed for sorting and high-content analysis of single cells using dielectrophoresis. It makes high-resolution imaging of suspended cells feasible immediately before depositing them into a microtiter plate. The microfluidic devices contain three-dimensional arrangements of radio-frequency driven electrodes and are used to gently manipulate suspended cells in flow. Viability of sorted and deposited cells is comparable to a control group. The influence of RF electric fields is studied using (a) calcium flux measurements and membrane potential dependent fluorescence dye on suspended human cells and (b) cultivation of yeast trapped for several days in dielectric field cages driven at field strengths up to 100 kV/m and 7 MHz.

Dielectrophoretic manipulation of suspended submicron particles

Planar and three‐dimensional multi‐electrode systems with dimensions of 2 — 40 μm were fabricated by IC technology and used for trapping and aggregation of microparticles. To achieve negative dielectrophoresis (repelling forces) in aqueous solution, radiofrequency (RF) electric fields were used. Experimentally, particles down to 100 nm in diameter were enriched and trapped as aggregates in field cages and dielectrophoretic microfilters and observed using confocal fluorimetry. Theoretically, single particles with an effective diameter down to about 35 nm should be trappable in micron field cages. Due to the unavoidable Ohmic heating, RF electric fields can induce liquid streaming in extremely small channels (12 μm in height). This can be used for pumping and particle enrichment but it enhances Brownian motion and counteracts dielectrophoretic trapping. Combining Brownian motion with ratchet‐like dielectrophoretic forces enables the creation of Brownian pumps that could be used as sensitive separation devices for submicron particles if liquid pumping is avoided in smaller structures.

MICRODEVICE FOR CELL AND PARTICLE SEPARATION USING DIELECTROPHORETIC FIELD-FLOW FRACTIONATION

We describe the use of a micro system for dielectrophoretic field flow fractionation (DFFF) of particles and cells. Micro-objects are separated on the basis of differences in size and/or passive dielectric properties, respectively. Bow-like strip electrode pairs have been proven to be the most effective separation systems.