A novel approach to dielectrophoresis using carbon electrodes

Abstract

Carbon-electrode dielectrophoresis (carbon-DEP) is demonstrated here as an alternative to more traditional DEP techniques. Carbon-DEP combines advantages of metal-electrode and insulator-based DEP by using low-cost fabrication techniques and low voltages for particle manipulation. The use of 3-D electrodes is proved to yield significant advantages over the use of traditional planar electrodes. This paper details the fabrication of dense arrays of tall high aspect ratio carbon electrodes on a transparent fused-silica substrate. The shrinkage of the SU-8 structures during carbonization is characterized and a design tool for future devices is provided. Applications of carbon electrodes in DEP are then detailed and include particle positioning, high-throughput filtering and cell focusing using positive-DEP. Manipulated cells include Saccharomyces cerevisiae and Drosophila melanogaster. The advantages and disadvantages of carbon-DEP are discussed at the end of this work.

Fifty years of dielectrophoretic cell separation technology

“…This can be done virtually, by using electrodes above and below the channel to create a volume effect, 41 or physically; 3D electrodes in this manner have been created by the use of electroplating to "grow" electrodes across the channel, 42 or by carbonization of complex pillar shapes formed from the photoresist SU-8. 43 A third approach used vertical traveling-wave dielectrophoresis electrodes, effectively producing a novel field effect for FFF. 44 An third approach to 3D electrode structures requiring no microfabrication at all was demonstrated by Fatoyinbo et al 45 and expanded on by Azhar Razak, 46 where electrodes were formed from a laminate of conducting and insulating sheets through which holes are drilled-forming many channels, each with electrodes "striped" down the inside.…”

SU-8 Photolithography as a Toolbox for Carbon MEMS

“…Lower doses minimize the chance of starting a cross-linking reaction in the narrow gaps between high aspect ratio structures due to light diffraction. A recommended initial value based on this author's work is 180 mJ/cm 2 for layer thicknesses up to 200 µm followed by a 60-min post-exposure bake at 95 °C [31]. Note that the baking time is increased with respect to that recommended in the datasheet to ensure complete cross-linking.…”

Enrichment of diluted cell populations from large sample volumes using 3D carbon-electrode dielectrophoresis

“…The fabrication procedure has been detailed several times before. 37,38,41,49 Briefly, microstructures were fabricated by a two-step photolithography process of SU-8 (Gersteltec, Switzerland), a negative-tone photoresist, on a silicon wafer. These structures were then carbonized by heat treatment to 1000 C in a nitrogen atmosphere.…”

“…40 The advantages and disadvantages of using carbonDEP over other DEP techniques have been detailed several times before. 22,29,41,42 Briefly, the fabrication of 3D electrodes is relatively low cost and straightforward; carbon has a wider electrochemical stability window than noble metals which reduces the chance of sample electrolysis for a given applied voltage; and carbon offers excellent chemical inertness and biocompatibility. Although the electrical conductivity of glassy carbon is less than that of metals, it is in the same order of indium tin oxide, [43][44][45] and an effective DEP force can be generated by polarizing the carbon electrodes with tens of volts.…”