(8e) C-MEMS Based Electrodes for the Dielectric Characterization of Microparticles Employing Dielectrophoresis

Víctor H. Pérez-González,^1,2 Vinh Ho,² Lawrence Kulinsky,² Blanca H. Lapizco-Encinas,³ Marc Madou,^2,4 Sergio O. Martínez-Chapa,¹*

1 BioMEMS Research Chair, Tecnológico de Monterrey, Monterrey, NL, México.

2 Mechanical & Aerospace Engineering, University of California, Irvine, Irvine, CA, US.

3 Microscale Bioseparations Laboratory and Department of Chemical Engineering, Tennessee Technological University, Cookeville, TN, US.

4 Ulsan National Institute of Science and Technology, World Class University Program, Ulsan 689-79, South Korea.

*Correspondence author. Email: smart@itesm.mx

Dielectrophoresis (DEP), the translational motion of polarizable particles exposed to a non-uniform electrical field, is an electrokinetic technique that has gained importance in the last two decades within the microfluidic research community. DEP can be employed to perform manipulation, isolation, filtration, focusing, characterization, or concentration of microparticles. The efficiency of dielectrophoresis is directly related to the distribution of the electrical field that can be controlled by the geometric design of the electrodes. An AC signal is applied to carry out a dielectrophoretic experiment. In order to optimize the DEP process for particle manipulation (especially for particles with unknown dielectric properties), a frequency sweep is performed to find the frequency range in which the particle can be manipulated effectively. When information about the dielectric properties of particles is readily available, mathematical modeling can be used to find the desired frequency window before carrying out the experiment, saving time and resources. Through a-priori knowledge of the relative permittivity and electric conductivity of a particle and the medium, it is possible to optimize separation, isolation, manipulation or filtration processes based on DEP. The dielectric characterization of microparticles employing dielectrophoresis was covered in several works; nonetheless there are some problems yet to be solved. In particular, the uncontrolled distribution of the field nonuniformity within the device was demonstrated to affect the dielectric properties estimation. The geometry of the electrodes defines the dielectrophoretic response of the microparticles under analysis. For instance, if planar interdigitated electrodes are employed to induce DEP, the response of the particles will be of different magnitude depending on their spatial position in the microchannel – the field is stronger closer to the tips of electrodes, and weaker towards the center of the channel. This difference in dielectrophoretic response is a source of measurement uncertainty in characterization applications.

Carbon MEMS (C-MEMS) is a microfabrication process in which carbon microstructures are obtained through photolithography and pyrolysis of organic precursors. The C-MEMS process is especially useful in biotechnology applications because of the wide electrochemical stability and biocompatibility of carbon. Using C-MEMS process, three-dimensional (3D) electrodes can be fabricated, allowing for the development of new electrode geometries different from the widely used interdigitated fingers and polynomial electrodes. This work deals with the development of 3D electrode geometries employing the C-MEMS microfabrication process and construction of microfluidic platforms for the dielectric characterization of microparticles employing DEP. COMSOL Multiphysics was employed to analyze the distribution of the electrical field created by different electrode geometries. Simulation results informed the optimized design of 3D Carbon electrodes. Carbon electrodes were fabricated based on the C-MEMS process, and microfluidic channel were created in PDMS or patterned with adhesive layers. Polystyrene microparticles with diameters ranging from 500 nm to 4 µm were used to test the characterization platform. Videos were recorded from the experiments to measure particle velocities. Information about particle velocity was then combined with COMSOL predictions of the electrical-field-squared gradient. This allowed for solving a set of nonlinear equations with the relative permittivity and electric conductivity of the particles as unknown variables. Applications of this work include environmental screening for water contamination, improvements of clean energy production methods, clinical analysis and food safety contol, among others.