(72d) A Novel Approach to Dielectrophoresis Using Carbon Electrodes

Carbon-electrode Dielectrophoresis (CarbonDEP) is a technique that employs carbon structures or surfaces as electrodes to induce DEP. The use of carbon as electrode material offers several advantages which make it a more suitable material than those used in DEP. The traditional method to induce DEP has been based on the use of metal electrodes. Advantage of this approach is the obtainment of high electric field gradients employing low applied voltages. However, the use of metal electrodes must obey a limit on the magnitude of the voltage applied in order to prevent sample electrolysis. Fabrication-wise, even when the fabrication of planar metal electrodes is relatively easy and readily achievable is not the same case when fabricating 3D electrodes. 3D structures require the use of more complicated techniques such as electroplating that might not result in high fabrication yields and lead to expensive devices. An alternative to metal electrodes is the use of insulator-based DEP (iDEP). In this technique a uniform electric field is applied across an array of insulating structures. The presence of these structures will then distort the electric field rendering it non uniform around the insulating structures. The possibility of electrolyzing the sample reduces greatly in iDEP, since the majority of the sample is in contact with an insulating material. Furthermore, insulating structures can be readily fabricated in planar or 3D shapes with fabrication techniques that do not require infrastructure as expensive as metal deposition equipment. Unfortunately, one of the primary drawbacks of an iDEP system is the requirement of a high electric field which can cause significant Joule heating and damage biological particles. Additionally, iDEP depends greatly on sample composition, in order to avoid joule heating only low-conductivity samples can be used. CarbonDEP combines the advantages of metal-based and insulator-based DEP. Even when carbon conductivity is lower than that of metals high-magnitude electric fields can still be induced with voltages in the range of units of volts. Thanks to the C-MEMS technique (the carbonization of previously micropatterned organic polymers), carbon electrodes, including 3D, can be fabricated with high yield and without the need of expensive infrastructure. The use of carbon brings further advantages: 1) Carbon was wider electrochemical stability window than gold or platinum meaning that more voltage might be applied to carbon electrodes immersed in a given solution without inducing electrolysis in the solution, 2) excellent biocompatibility, 3) carbon is chemically inert to mostly all solvents and 4) has excellent mechanical properties. This novel manner for carrying out DEP allows for inexpensive and efficient particle manipulation. This work presents the state-of-the-art on CarbonDEP. Previous work includes the discrimination of viable yeast cells from non viable ones, the filtration of yeast cells against a flow and the selectively position of latex particles. Extensive modeling and simulation work has also been conducted. Furthermore it has also been demonstrated how the use of 3D electrodes yields better throughputs than planar electrodes. CarbonDEP has also been integrated on a rotating platform towards a sample-to-result platform for clinical and diagnostics applications.