AC electrokinetics is rapidly becoming a foundational tool for lab-on-a-chip systems due to its versatility and the simplicity of the components capable of generating them. Predicting the behavior of fluids and particles under non-uniform AC electric fields is important for the design of next generation devices. Though there are several important phenomena that contribute to the overall behavior of particles and fluids, current predictive techniques consider special conditions where only a single phenomenon may be considered. We report a 2D numerical simulation, using COMSOL Multiphysics, which incorporates the three major AC electrokinetic phenomena (dielectrophoresis, AC electroosmosis and electrothermal effect) and is valid for a wide range of operational conditions. Corroboration has been performed using experimental conditions that mimic those of the simulation and shows good qualitative agreement. Furthermore, a broad range of experiments has been performed using four of the most widely reported devices under varying conditions in order to show their behavior as it relates to the simulation. The large number of experimental conditions reported, together with the comprehensive numerical simulation, will help provide guidelines for scientists and engineers interested in incorporating AC electrokinetics into their lab-on-a-chip systems.

Abbreviations: (PEEK) polyetheretherketoneKeywords: accuracy, dose, glycemic, insulin, pump, variability

The field of AC electrokinetics is rapidly growing due to its ability to perform dynamic fluid and particle manipulation on the micro-and nano-scale, which is essential for Lab-on-a-Chip applications. AC electrokinetic phenomena use electric fields to generate forces that act on fluids or suspended particles (including those made of dielectric or biological material) and cause them to move in astonishing ways 1, 2 . Within a single channel, AC electrokinetics can accomplish many essential on-chip operations such as active micro-mixing, particle separation, particle positioning and micro-pattering. A single device may accomplish several of those operations by simply adjusting operating parameters such as frequency or amplitude of the applied voltage. Suitable electric fields can be readily created by micro-electrodes integrated into microchannels. It is clear from the tremendous growth in this field that AC electrokinetics will likely have a profound effect on healthcare diagnostics 3-5 , environmental monitoring 6 and homeland security 7 .In general, there are three AC Electrokinetic phenomena (AC electroosmosis, dielectrophoresis and AC electrothermal effect) each with unique dependencies on the operating parameters. A change in these operating parameters can cause one phenomena to become dominant over another, thus changing the particle or fluid behavior.It is difficult to predict the behavior of particles and fluids due to the complicated physics that underlie AC electrokinetics. It is the goal of this publication to explain the physics and elucidate particle and fluid behavior. Our analysis also covers how to fabricate the electrode structures that generate them, and how to interpret a wide number of experimental observations using several popular device designs. This video article will help scientists and engineers understand these phenomena and may encourage them to start using AC Electrokinetics in their research. Video LinkThe video component of this article can be found at http://www.jove.com/details.php?id=813 ProtocolFabricating Cr/Au Electrodes on Glass Substrates Part 1A: Wet Etch Method *For the highest quality devices, the fabrication process should be performed in a clean room environment or under laminar flow hoods so that dust and other contaminants won't affect the pattern. 3. Shipley 1827 positive photoresist is deposited on the glass slides with a spincoater (3000 rpm, 1000 rpm/s ramp, 30 second spin time). 4. Substrates are then soft baked for 2 minutes at 100°C. 5. The pattern of the mask is transferred to the photoresist with contact UV exposure for 8.4 seconds for a total of 206 mJ/cm 2 . 6. The photoresist is developed in Microposit MF 351:Water (1:3) for 30 seconds with good agitation followed by a DI water rinse. 7. After inspection with a microscope to ensure good development, the substrates are then etched in Au Etchant and Chrome etchant for 15 seconds and 30 seconds respectively with DI washes in between and after.1. 2-inch by 4-inch Glass slides are placed in a heated (80...

Ac electrokinetics is a versatile technique for particle and fluid manipulation in microfluidic environment. However, analyzing and predicting particle motions due to the ac electrokinetic effects is a difficult task because it requires the quantitative understanding of multiple phenomena such as dielectrophoresis (DEP), ac electroosmosis (ACEO), and electrothermal effects (ETE). In this paper we present a force balance approach to analyze ac electrokinetic effects, particularly ACEO. Pressure-driven flows were used to quantify the ACEO and DEP forces acting on a particle. Polystyrene microbeads suspended in KCl solution were introduced in polydimethylsiloxane (PDMS) microchannels attached to a glass plate with gold microelectrodes. The microbeads were initially collected and aligned along the center of the electrodes at 1 kHz and 1 Vp-p, and then a well-controlled pressure-driven flow was introduced resulting in the translation of the particles. Particles moved to a new location where a new force balance is reached. This particle translation on the surface of the electrode was carefully monitored as varying the applied flow rate. The net force due to ac electrokinetic effects at different locations over the electrode was calculated using the experimental data and the force balance relationship.

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