Dielectrophoretic Concentration and Separation of Live and Dead Bacteria in an Array of Insulators

Abstract

Insulator-based (electrodeless) dielectrophoresis (iDEP) is an innovative approach in which the nonuniform electric field needed to drive DEP is produced by insulators, avoiding problems associated with the use of electrodes. Live and dead Escherichia coli were concentrated and selectively released by applying stepped DC voltages across a microchannel containing an array of insulating posts etched in glass. The only electrodes present were two platinum wires placed in the inlet and outlet reservoirs, producing mean electric fields of up to 200 V/mm across the insulators. The cells were labeled with Syto 9 and propidium iodide and imaged through a fluorescent microscope. Cell trapping and release were controlled by modifying the relative responses of electrokinesis and DEP by adjusting the magnitude of the applied voltage. Dead cells were observed to have significantly lower dielectrophoretic mobility than live cells, whereas the electrokinetic mobilities of live and dead cells were indistinguishable. The locations of the bands of differentially trapped cells were consistent with predictions. In addition, cells were selectively trapped and concentrated against backgrounds of 1- and 0.2-microm carboxylate-modified polystyrene particles. This first application of iDEP for simultaneous live/dead bacteria separation and concentration illustrates its potential as a front-end method for bacterial analysis.

Fifty years of dielectrophoretic cell separation technology

“…The particles then interact with these field non-homogeneities, collecting or being repelled from them; in a difference from the typical arrangement in electrode-based devices, negative dielectrophoresis is commonly used to trap particles in the device, where a highly repulsive field between the electrodes creates a barrier between the posts which cells experiencing negative DEP are unable to cross. Cells which experience a weaker repulsive or attractive force (which can be overcome by the flow) pass through the device and can be collected, and the setup has been used for bacteria 37 and mammalian cells, 38 though separations are commonly of the "live/dead" variety, and bacteria feature widely. Partially, this may be due to the very high voltages (and concomitant Joule heating) associated with substantial voltages, though recent designs 39 have been published to reduce this.…”

Low level epifluorescent detection of nanoparticles and DNA on dielectrophoretic microarrays

“…A related technology, dielectrophoresis (DEP), has proven to be a robust separation and concentration technique for microscopic and nanoscopic bioparticles [19], including human cancer and blood cells [20][21][22][23], bacteria [24][25][26], virus [27], and DNA [28]. DEP is an electrokinetic process in which particles placed in an asymmetric electric field can be separated by an alternating [29] or constant [30] voltage signal.…”

Tuning direct current streaming dielectrophoresis of proteins

“…4 Another approach is insulator-based DEP (iDEP), in which electric field gradients are created by integrating nonconductive obstacles in a microfluidic device. [4][5][6] In iDEP, the application of electric potentials via electrodes immersed in the microdevice reservoirs allows the decoupling of electrode effects within the large reservoir volume. The technique requires larger applied potentials to achieve high electric fields within the microdevice but establishes homogeneous electric fields throughout the entire depth of the microfluidic channel.…”