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Surface microfluidics—high-speed DEP liquid actuation on planar substrates and critical factors in reliable actuation

Analysis of chemical and biological samples requires one or more of the following sequential steps: sampling, sample transport, sample pretreatment and sample processing. As a result of miniaturization, such total analysis systems offer manifold advantages such as mass production, portability and hence on-site operation, ease of use, low sample consumption and high stability. In this regard, dielectrophoretic (DEP) liquid actuation, in recent years, has emerged as an attractive technique for microfluidic systems since it provides simple, robust sample handling capabilities. This study experimentally examines the impact of more critical device structural features and material properties on the performance and reliability of the liquid DEP actuation. Specifically, we investigated the impact of electrode material (gold-chrome versus aluminum), various dielectric materials, and thicknesses on the DEP actuation voltage (minimum), DEP actuated finger transport dynamics and subsequent droplet formation. Both the voltage requirements for DEP liquid finger actuation and subsequent liquid finger transport are in good agreement with the theoretical predictions of the lumped-parameter dynamic model proposed by Jones (2001 Proc. 4th Int. Conf. on Applied Electrostatics). Furthermore, the dynamics of the finger is influenced by the radius of finger, which is controlled by the width and spacing of the electrodes. For the smaller electrode geometry, the finger dynamics is viscosity dominated; exhibiting t1/2 dependence however for larger finger radius inertia appears to dominate the finger dynamics. The utility of DEP in actuating protein (Taq enzyme) samples was examined and observed to be limited by the specific protein adsorption.