AC Electroosmosis Flow Research Articles

A study on an AC electroosmotic micropump using a square pole – Slit electrode array

The paper presents a novel AC electroosmotic micropump using a square pole – slit electrode array called the SS-ACEO-MP. The AC electroosmosis (ACEO) generates convection flows when AC voltage is applied to a liquid such as water with fixed electrodes. The ACEO flow is stable without electrolysis due to the low AC voltage; however, to realize a micropump for wide applications, a special mechanism for a unidirectional flow is required. For that purpose, conventional devices utilize asymmetric electrodes, induced-charge electroosmosis, and traveling wave voltage. For practical applications, high slip velocity due to ACEO is required. The proposed pump consists of a square pole – slit electrode array, and efficiently generates a total flow by the slip velocity mainly on the slit electrodes. The proposed pump features a simple pillar-shaped structure without moving parts, efficient flow generation, and easy improvements of the pressure and the flow rate due to the arrayed structure. First, 3D FEM (finite element method) simulation of the SS-ACEO-MPs was performed and the characteristics were clarified. The size parameters that maximize the effective slip velocity under no load were clarified. Second, the SS-ACEO-MPs were fabricated by a MEMS (micro electro mechanical systems) fabrication process that included electroforming. Third, experiments on the SS-ACEO-MPs were performed. The characteristics of the SS-ACEO-MPs were clarified. Finally, at the applied voltage of 26Vpp, the maximum effective slip velocity of 1.6mm/s was realized with a unit size of 0.2×0.2×0.05mm3.

Accelerated insulin aggregation under alternating current electric fields: Relevance to amyloid kinetics.

The time-dependent nucleation phase is critical to amyloid fibrillation and related to many pathologies, in which the conversion from natively folded amyloidogenic proteins to oligomers via nucleation is often hypothesized as a possible underlying mechanism. In this work, non-uniform AC-electric fields across two asymmetric electrodes were explored to control and examine the aggregation of insulin, a model amyloid protein, in aqueous buffer solution at constant temperature (20 °C) by fluorescence correlation spectroscopy and fluorescence microscopy. Insulin was rapidly concentrated in a strong AC-field by imposed AC-electroosmosis flow over an optimal frequency range of 0.5-2 kHz. In the presence of an AC-field, direct fibrillation from insulin monomers without the formation of oligomer precursors was observed. Once the insulin concentration had nearly doubled its initial concentration, insulin aggregates were observed in solution. The measured lag time for the onset of insulin aggregation, determined from the abrupt reduction in insulin concentration in solution, was significantly shortened from months or years in the absence of AC-fields to 1 min-3 h under AC-fields. The ability of external fields to alter amyloid nucleation kinetics provides insights into the onset of amyloid fibrillation.

마이크로 채널 내 유도-전하 전기삼투에 의한 혼합

Abstract. This paper presents an experimental study on the performance of a micro-mixer using AC elec-tro-osmotic flow. The microchannel is made of PDMS for the side and top walls and glass patterned withITO for the bottom wall. We first investigated the effect of the applied potential as well as the frequencyon the slip velocity. We have found that the slip velocity is roughly proportional to the applied voltagein line with the Helmholtz-Smoluchowski equation and there is an optimum frequency at which the slipvelocity becomes maximized. To find the optimum parameters for mixing device we tested our devicefor various design parameters. It turned out that the best mixing effect is obtained approximately whenthe electrode angle is 30 o , electrode width 200µm, and the frequency of power supply 700 Hz. Key Words: AC Electro-osmosis flow(교류전기삼투 유동), Flow visualization(유동가시화 ), Mixing index(혼합지수 ), Optimum design(최적설계) 1. Introduction Lab-on-chips receive increasing attention in view oftheir possibility of practical applications in broad areassuch as biology and chemistry. Lab-on-chips arecomposed of micro-size mechanical and electricalsystems which enable pumping, mixing, separation,sequencing, reaction and even cell growth.Characterized by very low Reynolds numbers, thesystem encounters difficulty in mixing of fluids. Inorder to enhance mixing, various ideas have beenproposed in the literature. Cha et al.

A parametric study of AC electrothermal flow in microchannels with asymmetrical interdigitated electrodes

In this study, the AC electrothermal (ACET) flow in a microchannel with asymmetrical planar electrode pairs, in the same configuration as an AC electroosmosis (ACEO) pump, is studied numerically. The electrical, temperature and velocity fields in the microchannel are obtained by solving the coupled electrical, momentum and energy equations. The effects of electrode size, gap and length ratios, electrical conductivity of electrolyte solution, thermal conductivity of microchannel base material, as well as voltage and the frequency of AC on ACET flow are investigated in details. It is found that in the operating frequency range of the ACEO pump, i.e. 100 Hz–100 kHz, the velocity of the ACET flow is frequency-independent and moves in the same direction as the ACEO flow, and effects of electrode size, gap and length ratios on flow velocity have the same trend as the ACEO flow. Because the ACET flow velocity is proportional to electrical conductivities of electrolyte solution linearly and to the fourth power of the applied voltage, while the ACEO flow velocity decreases with the increase of electrical conductivity of the electrolyte solution and is only proportional to the square of applied voltage, therefore the ACET flow should not be neglected in an ACEO pump for the cases of high conductivity of electrolyte solution and relatively high AC voltage where ACEO and ACET effects are comparable.

AN AFFINITY SENSOR IMPROVED BY EWOD ACTUATOR-BASED MICROFLUIDIC CHIP

We propose an improved immunoassay method with EWOD-based microfluidic biochip. Electro-wetting on dielectric (EWOD) is based on contact angle-changed phenomenon of droplet on the channel surface. The reactant-containing droplet can be moved from reservoir to a modified electrode area, which a stir function can be provided by controlling AC electro-osmosis flow (ACEOF). The immunochemistry reaction takes place on our modified area via electro-wetting actuation, and the signal from fluorescent or electrochemical impedance spectroscopy (EIS) was used to confirm the performance of designed element.

Rapid and selective concentration of microparticles in an optoelectrofluidic platform

We demonstrate rapid manipulation and selective concentration of microparticles using AC electrokinetics such as dielectrophoresis (DEP) and AC electro-osmosis (ACEO) in an optoelectrofluidic platform based on a liquid crystal display (LCD). When 10 V bias at 10 kHz was applied to the optoelectrofluidic device, only the 1 microm-diameter polystyrene particles were concentrated into the projected LCD image patterns and closely packed, forming the crystalline structure by ACEO flow, while the 6 microm-diameter particles were repelled by negative DEP forces. We have characterized this frequency-dependency of the optoelectrofluidic particle behavior according to the particle diameter. On the basis of these results, we can rapidly concentrate the 1 microm-diameter particles and separate them from the 6 microm particles, by applying an AC signal of 10 kHz frequency. This novel technique can be applied to rapidly concentrate, separate and pattern micro-/nanoparticles in many biological and chemical applications.