Dielectrophoresis (DEP) is the motion of a particle due to polarization effects in nonuniform electric fields. DEP is an electrokinetic transport mechanism that can be used to concentrate and separate particles. DEP is a nondestructive technique, with a great potential for the separation and concentration of bioparticles. Traditionally, DEP has been carried out employing arrays of microelectrodes to generate nonuniform electric fields. This approach is expensive due to the elevated cost of microelectrode fabrication, which makes high throughput systems economically unfeasible. An alternative is the technique called insulator-based DEP (iDEP). In this technique, nonuniform electric fields are created with an array of insulating structures, instead of electrodes. Insulating materials such as plastics have excellent malleability and can be mass replicated, providing for high-throughput and large-volume devices. The present study investigated the effect of bulk medium properties on the dielectrophoretic behavior of microparticles under iDEP, employing microdevices made from glass. Each microdevice contained several microchannels, and each microchannel contained an array of insulating cylindrical posts. Electric field was applied across the post array, creating regions of higher and lower electric field intensity. Prior to each experimental session, the microchannel was filled with a buffer solution of a known pH and conductivity. A sample of the microparticles was injected into the microchannel and an electric field was applied. The dielectrophoretic response of the particles was recorded in the form of videos and pictures. A parametric study was carried out by varying the pH and conductivity of the bulk medium, as well as the magnitude of the applied electric field, in order to study how each one of these parameters affects the dielectrophoretic response of the microparticles. It is anticipated that the results from this research project will provide with guidelines for the design and operation of insulator-based DEP devices for the concentration and separation of bioparticles.
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