Electrokinetic Velocity Characterization of Microparticles in Glass Microchannels

José I. Martínez-López1, Blanca H. Lapizco-Encinas1, Héctor Moncada-Hernández1, Marco Rito-Palomares1, and Sergio O. Martínez-Chapa2. (1) Biotechnology and Food Engineering and Electrical Engineering, Tecnologico de Monterrey, Ave Eugenio Garza Sada 2501, Col. Tecnologico, Monterrey, 64849, Mexico, (2) Electrical Engineering, Tecnologico de Monterrey, Ave Eugenio Garza Sada 2501, Col. Tecnologico, Monterrey, 64849, Mexico

Insulator-based dielectrophoresis (iDEP) an efficient technique with great potential for miniaturization. It has been applied successfully for the manipulation and concentration of a wide array of particles, including bioparticles such as macromolecules and microorganisms. When iDEP is applied employing DC electric fields, other electrokinetic transport mechanisms are present: electrophoresis and electroosmotic flow.

In order to achieve dielectrophoretic trapping of bioparticles, dielectrophoresis has to overcome electrokinetics (electroosmosis and electrophoresis). Therefore, in order to improve and optimize iDEP-based separations, it is necessary to characterize these electtrokinetics under the operating conditions employed for dielectrophoretic separations. The main objective of this work is to identify the operating conditions that will benefit dielectrophoretic trapping and concentration of particles when electrokinetics is present.

This study presents the estimation of the electrokinetic mobility of microparticles suspended inside a microchannel. Micro Particle Image Velcimetry (uPIV) was employed to measure the velocity of 1-um-diameter inert polystyrene particles suspended in a 3cm-long, 10-um deep, 1-mm-wide, straight glass microchannel. A parametric study was carried out by varying the properties of the suspending medium (conductivity and pH) as well as the strength of the applied DC electric field. The results obtained using uPIV allowed to identify the conditions under which the electrokinetic force (i.e. particle velocity) is lowest, i.e., optimal conditions for dielectrophoretic trapping. It was shown that high conductivity and low pH values for the suspending medium produce lower electrokinetic mobilities, i.e., low electrokinetic force, thus benefiting dielectrophoretic trapping. These findings were proved by carrying out dielectrophoretic trapping of microparticles employing a glass microchannel that contained cylindrical insulating structures. The results obtained in this study will provide with guidelines for the optimization of iDEP-based separations.