Research Article A novel approach to dielectrophoresis using carbon electrodes 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. Keywords: 3-D / Carbon / Dielectrophoresis / High throughput / Sorting DOI 10.1002/elps.201100059 1 Introduction Dielectrophoresis (DEP) is a technique for particle manipula- tion that exploits the interaction between an induced dipole and a non-uniform electric field. Most of the work on DEP has relied on the use of planar metal microelectrodes to create the required non-uniform electric field across a sample. Examples of the use of planar metal electrodes for DEP include the selective manipulation and sorting of blood cells, cancer cells and microorganisms [1–3]. However, planar electrodes on the channel surfaces generate only an electric field gradient close to the electrode and not throughout the bulk of the solution in the remainder of the fluidic channel. In contrast, the use of 3-D electrodes that cover the whole height of the channel allows for the addressing of all particles throughout the solution in the channel. Indeed, the use of 3-D electrodes minimizes the distance from a targeted particle to the nearest electric field gradient and thus reduces or eliminates altogether the number of re-flow cycles that may be required to improve throughput when using planar electrodes. Unfortunately, the fabrication of 3-D metal electrodes quickly turns complicated and expensive as it typically requires the use of metal electroplating which often limits the yield and results in more expensive devices. Examples on the use of electroplated gold structures for DEP applications include those by Wang et al. [4] who used them for 3-D cell focusing and by Voldman et al. [5] who used gold pillars to implement an interrogation site for flow cytometry applications. An alternative to metal-electrode DEP is insulator-based DEP or iDEP [6–8]. In this technique, metal macroelectrodes (for example, extruded wire rods or machined metal plates) are positioned on both ends of an array of insulating microstructures. A high voltage is then applied to the metal electrodes to create a uniform electric field between them that is rendered non-uniform in the vicinity of the insulator structures. iDEP allows for the low-cost fabrication of experimental devices since (i) no metal microelectrodes are required, (ii) the insulator structures, either 2-D or 3-D, are made of inexpensive materials such as glass or polymer and (iii) low-cost fabrication techniques such as injection mold- ing and embossing can be used. Another important advan- tage of iDEP over metal-electrode DEP is the reduced chance of sample electrolysis since the sample does not necessarily contact the metal electrodes. Unfortunately, iDEP requires very high voltages (electric field magnitude is inversely proportional to the gap between electrodes and in iDEP the separation between metal electrodes can be in the order of centimeters) to create a suitable electric field gradient for DEP, which increases the cost of the polarizing electronics and the hazard of electric shock during operation. Here, we present the use of carbon electrodes as an alternative to both metal-electrode DEP and iDEP. Carbon- electrode DEP or carbon-DEP combines the advantages of metal-based and insulator-based DEP: the fabrication of 3-D Rodrigo Martinez-Duarte 1,2 Philippe Renaud 2 Marc J. Madou 1,3 1 Department of Mechanical and Aerospace Engineering, University of California, Irvine, USA 2 Microsystems Laboratory (LMIS4), E ´ cole Polytechnique Fe ´ de ´ rale de Lausanne, Switzerland 3 Ulsan National Institute for Science and Technology, World Class University Program, South Korea Received January 22, 2011 Revised March 25, 2011 Accepted March 25, 2011 Colour Online: See the article online to view Figs. 1–6 in colour. Abbreviations: AR, aspect ratio; BSA, bovine serum albumin; FCS, fetal calf sera; carbon-DEP, carbon-electrode dielectrophoresis; DEP, dielectrophoresis; iDEP, insulator- based DEP; PC, polycarbonate; PSA, pressure-sensitive adhesive Correspondence: Dr. Rodrigo Martinez-Duarte, EPFL-STI-LMIS4, Station 17, CH-1015 Lausanne, Switzerland E-mail: drmartnz@gmail.com Fax: 141-21-693-5950 & 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.electrophoresis-journal.com Electrophoresis 2011, 32, 2385–2392 2385