Side-Wall Vertical Electrodes for Lateral Field Microfluidic Applications

This paper describes the design, fabrication, and testing of microfluidic devices enabled by electrodes embedded vertically in the side walls of SU-8 microchannels. With vertical electrodes on the side walls, one can generate higher lateral electrical fields uniform along the vertical direction in the channel (perpendicular to the substrate). By designing the electrode shapes and configurations, uniform and nonuniform electrical fields in the lateral (planar) directions can be applied to manipulate flow or particles in microchannels for switching or sorting applications. The uniform field is demonstrated in a magnetohydrodynamic (MHD) microfluidic device for directing cells to different channel outlets while the nonuniform field is demonstrated in the generation of dielectrophoresis (DEP) forces for microbead focusing. Metal electrodes are fabricated by electroplating to form vertical electrodes aligned with the channel walls. The multilayer SU-8 lithography technique enables the four walls of the channel to be all SU-8. The thin precoated SU-8 layer on the substrate improves structure integrity of the SU-8 microchannels. The mechanical flexibility of PDMS compensates for the surface nonuniformity from the previous patterning steps to conformably cap the channel. The ability to integrate versatile electrodes design broadens the realm of electrical control and sensing for microfluidic applications