Article

A self-contained acoustofluidic platform for biomarker detection

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Abstract

Self-contained microfluidic platforms with on-chip integration of flow control units, microreactors, (bio)sensors, etc. are ideal systems for point-of-care (POC) testing. However, current approaches such as micropumps and microvalves, increase the cost and the control system, and it is rather difficult to integrate into a single chip. Herein, we demonstrated a versatile acoustofluidic platform actuated by a Lamb wave resonator (LWR) array, in which pumping, mixing, fluidic switching, and particle trapping are all achieved on a single chip. The high-speed microscale acoustic streaming triggered by the LWR in the confined microchannel can be utilized to realize a flow resistor and switch. Variable unidirectional pumping was realized by regulating the relative position of the LWR in various custom-designed microfluidic structures and adoption of different geometric parameters for the microchannel. In addition, to realize quantitative biomarker detection, the on-chip flow resistor, micropump, micromixer and particle trapper were also integrated with a CMOS photo sensor and electronic driver circuit, resulting in an automated handheld microfluidic system with no moving parts. Finally, the acoustofluidic platform was tested for prostate-specific antigen (PSA) sensing, which demonstrates the biocompatibility and applied potency of this proposed self-contained system in POC biomedical applications.

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... [29] In contrast, Wu et al. directly placed C-shaped interdigital transducers (IDTs) within a triangle-edged microchannel (Figure 2e) to generate local SAW-induced streaming and further form unidirectional liquid motion with a flow rate between 18.5 and 41.5 nL/min. [30] As shown in Figure 2f, a recent work by Duan's group designed an "L-shaped" microchannel with a right angle included to match the propagation direction of the Lamb wave, such that one of the acoustic streaming jets of the LWR was maintained while the backflow was minimized; this design led to unidirectional pumping with a dynamic flow rate from 1 to 30 μL/min under low power consumption (0.05-0.1 W). [31] ...
... Chen et al. recently designed an acoustic micro flow resistor by placing an LWR in a straight channel, and there existed a hedging trend between the acoustic streaming jet and the external flow. [31] Based on the regulation of applied acoustic power, the flow resistance was finely controlled when the external flow rate was fixed. Furthermore, a flow channel (two inlets and one outlet) assembled with two LWRs was demonstrated to be a dynamic flow switch (Figure 3b), and the liquid in the main channel was successfully changed by tuning the acoustic power of the LWR in the branch channel. ...
... [50] Another versatile acoustofluidic platform actuated by an LWR array possesses the manipulation functions of mixing, pumping, fluidic switching and particle trapping in a single chip, and a CMOS photosensor and an electronic driver circuit were integrated with this acoustofluidic chip, resulting in an handheld diagnostic device (4.4 cm×10 cm×18.7 cm) to accomplish quantitative biomarker detection, which demonstrates the vital and meaningful value in POCT applications ( Figure 7). [31] ...
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... Unlike passive pumps, active pumps offer better flexibility in fluid manipulation. Typical active pumps include optically driven pumps [11,12], electric pumps [13,14], magnetic pumps [9,10], pneumatic membrane pumps, and acoustic pumps [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34]. ...
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Tuberculosis (TB) remains the high-risk infectious pathogen that caused global pandemic and high mortality, particularly in the areas lack in health resources. Clinical TB screening and diagnosis are so far mainly conducted on limited types of commercial platforms, which are expensive and require skilled personnel. In this work, we introduced a low-cost and portable finger-driven microfluidic chip (named Fd-MC) based on recombinase polymerase amplification (RPA) for rapid on-site detection of TB. After injection of the pre-treated sample solution, the pre-packaged buffer was driven by the pressure generated by the finger-actuated operation to accomplish sequential processes of diagnosis in a fully isolated microchannel. An in-situ fluorescence strategy based on FAM-probe was implemented for on-chip results read-out though a hand-held UV lamp. Hence, the Fd-MC proved unique advantageous for avoiding the risk of infection or environmental contamination. In addition, the Fd-MC was designed for multiplexed detection, which is able to not only identify TB/non-TB infection, but also differentiate between human Mycobacterium tuberculosis and Mycobacterium bovis. The platform was verified in 37 clinical samples, statistically with 100% specificity and 95.2% sensitivity as compared to commercial real-time RPA. Overall, the proposed platform eliminates the need on external pumps and skilled personnel, holding promise to POC testing in the resource-limited area.
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Microfluidics drives technological advancement in point-of-care (POC) bioanalytical diagnostics towards portability, fast response and low cost. In most microfluidic bioanalytical applications, flowing antigen/antibody reacts with immobilized antibody/antigen at a constant flux; it is difficult to reach a compromise to simultaneously realize sufficient time for the antigen–antibody interaction and short time for the entire assay. Here, we present a pump-free microfluidic chip, in which flow is self-initialized by capillary pumping and continued by imbibition of a filter paper. Microfluidic units in teardrop shape ensure that flow passes through the reaction areas at a reduced flux to facilitate the association between antigen and antibody and speeds up after the reaction areas. By spotting different antibodies into the reaction area, four types of biomarkers can be measured simultaneously in one microfluidic chip. Moreover, a small-sized instrument was developed for chemiluminescence detection and signal analysis. The system was validated by testing four biomarkers of colorectal cancer using plasma samples from patients. The assay took about 20 minutes. The limit of detection is 0.89 ng mL⁻¹, 1.72 ng mL⁻¹, 3.62 U mL⁻¹ and 1.05 U mL⁻¹ for the assays of carcinoembryonic antigen, alpha-fetoprotein, carbohydrate antigen 125 and carbohydrate antigen 19-9, respectively. This flux-adaptable and self-contained microfluidic platform is expected to be useful in various POC disease-monitoring applications.
Article
Acoustofluidics have been widely used for particle and cell manipulations. Given the scaling of acoustic radiation forces and acoustic streaming flow velocities with increasing frequency, existing acoustofluidic manipulation of submicron particles require actuation at MHz and even GHz frequencies. In this work, we explore a novel acoustofluidic phenomenon, where an ultra-low frequency (800 Hz) acoustic vibration is capable of concentrating and patterning submicron particles at two poles of each pillar in an array embedded in a microfluidic device. This unprecedented phenomenon is attributed to a collective effect of acoustic streaming induced drag force and non-Newtonian fluid induced elastic lift force, arising from symmetric acoustic microstreaming flows around each pillar uniformly across the entire pillar array. To our knowledge, this is the first demonstration that particles can be manipulated by an acoustic wave with a wavelength that is six orders of magnitude larger than the particle size. This ultra-low frequency acoustofluidics will enable a simple and cost-effective solution to effective and uniform manipulation of submicron biological particles in large scales, which has the potential to be widely exploited in clinical and biomedical fields.
Article
Exosomes, a form of extracellular vesicle, are an important precursor in regenerative medicine. Microfluidic methods exist to capture these sub-micrometer sized objects from small quantities of sample, ideal for multiple diagnostic applications. To address the challenge of extraction from large volumes, we use the visual access offered by microfluidic techniques to probe the physical mechanisms behind a method which is compatible with future upscaling. The sound wave actuated nano-sieve uses resonant modes in a packed bed of microparticles to exert trapping forces on nanoparticles. Here, we examine the role of the microparticle size, demonstrating better performance from 15 um particles than 7 um particles. When applied to biological samples, we demonstrate for the first time that a packed bed of these larger particles is capable of capturing exosomes and liposomes, the captured particles being on average 20 to 40 times smaller than the pores within the trapped bed.
Article
The requirement of on-demand microfluidic pumps and instrument-free readout methods remains major challenges for the development of microfluidics. Herein, a new type of microfluidic platform, an on-demand photothermal microfluidic pumping platform, has been developed using the on-chip nanomaterial-mediated photothermal effect as the novel and remotely tunable microfluidic driving force. The photothermal microfluidic pumping performance can be adjusted remotely by tuning the irradiation parameters, without changing on-chip parameters or replacing enzyme or other reagents. In contrast to graphene oxide, Prussian blue nanoparticles with stronger photothermal conversion efficiency were used as the model photothermal agent to demonstrate the proof of concept. The on-chip pumping distance is linearly correlated with both the irradiation time and the nanomaterial concentration. The applications of the photothermal microfluidic pumping have been demonstrated in multiplexed on-chip transport of substances such as gold nanoparticles and visual quantitative bar-chart detection of cancer biomarkers without using specialized instruments. Upon the contact-free irradiation by a laser pointer, the strong on-chip nanomaterial-mediated photothermal effect can serve as a robust and remotely tunable microfluidic pump in a PMMA/PDMS hybrid bar-chart chip to drive ink bars in a visual quantitative readout fashion. This is the first report of the photothermal microfluidic pumping platform, which has great potential for various microfluidic applications.
Article
The integration of acoustics and microfluidics (termed acoustofluidics) presents a frontier in the engineering of functional micro-/nanomaterials. Acoustofluidic techniques enable active and precise spatiotemporal control of matter, providing great potential for the design of advanced nanosystems with tunable material properties. In this work, we introduce an acoustofluidic approach for engineering multifunctional three-dimensional nanostructure arrays and demonstrate their potential in enrichment and biosensing applications. In particular, our acoustofluidic device integrates an acoustic transducer with a sharp-edge-based acoustofluidic reactor that enables uniform patterning of zinc oxide (ZnO) nanoarrays with customizable lengths, densities, diameters, and other properties. The resulting ZnO nanoarray-coated glass capillaries can rapidly and efficiently capture and enrich biomolecules with sizes ranging from a few nanometers to several hundred nanometers. In order to enable the detection of these biomolecules, silver (Ag) nanoparticles are deposited onto the ZnO nanoarrays, and the integrated ZnO-Ag capillary device functions as a label-free plasmonic biosensing system for surface-enhanced Raman spectroscopy (SERS) based detection of exosomes, DNA oligonucleotides, and E. Coli bacteria. The optical sensing enhancement of ZnO-Ag capillary is further validated through finite-difference time-domain (FDTD) simulations. These findings not only provide insights into the engineering of functional micro-/nanomaterials using acoustofluidics, but also shed light onto the development of portable microanalytical devices for point-of-care applications.
Article
Separation of nano/microparticles based on surface acoustic waves (SAWs) has shown great promise for biological, chemical, and medical applications ranging from sample purification to cancer diagnosis. However, the permanent bonding of a microchannel onto relatively expensive piezoelectric substrates and excitation transducers renders the SAW separation devices non-disposable. This limitation not only requires cumbersome cleaning and increased labor and material costs, but also leads to cross-contamination, preventing their implementation in many biological, chemical, and medical applications. Here, we demonstrate a high-performance, disposable acoustofluidic platform for nano/microparticle separation. Leveraging unidirectional interdigital transducers (IDTs), a hybrid channel design with hard/soft materials, and tilted-angle standing SAWs (taSSAWs), our disposable acoustofluidic devices achieve acoustic radiation forces comparable to those generated by existing permanently bonded, non-disposable devices. Our disposable devices can separate not only microparticles but also nanoparticles. Moreover, they can differentiate bacteria from human red blood cells (RBCs) with a purity of up to 96%. Altogether, we developed a unidirectional IDT-based, disposable acoustofluidic platform for micro/nanoparticle separation that can achieve high separation efficiency, versatility, and biocompatibility.
Article
Agglutination is an antigen–antibody reaction with visible expression of aggregation of the antigens and their corresponding antibodies. Applications extend to the identification of acute bacterial infection, hemagglutination, such as blood grouping, and diagnostic immunology. Our finger-powered agglutination lab chip with external CMOS image sensing was developed to support a platform for inexpensive, rapid point-of-care (POC) testing applications related to agglutination effects. In this paper, blood grouping (ABO and Rh grouping) was utilized to demonstrate the function of our finger-powered agglutination lab chip with CMOS image sensing. Blood antibodies were preloaded into the antibody reaction chamber in the lab chip. The blood sample was pushed through the antibody reaction chamber using finger-powered pressure actuation to initiate a hemagglutination reaction to identify the blood type at the on-chip detection area using our homemade CMOS image sensing mini-system. Finger-powered actuation without the need for external electrical pumping is excellent for low-cost POC applications, but the pumping liquid volume per finger push is hard to control. In our finger-powered agglutination lab chip with CMOS image sensing, we minimized the effects of different finger push depths and achieved robust performance for the test results with different push depths. The driving sample volume per finger push is about 0.79 mm³. For different chips and different pushes, the driven sample volume per finger push was observed to vary in the range of 0.64 to 1.18 mm³. The red blood cells were separated from the plasma on-chip after the whole blood sample was finger pumped and before the red blood cells reached the antibody chamber via an embedded plasma-separation membrane. Our homemade CMOS image mini-system robustly read and identified the agglutination results on our agglutination lab chip.
Article
The precise transportation of small-volume liquids in microfluidic and nanofluidic systems remains a challenge for many applications, such as clinical fluidical analysis. Here, we present a reliable digital pump that utilizes acoustic streaming induced by localized fluid-substrate interactions. By locally generating streaming via a C-shaped interdigital transducer (IDT) within a triangle-edged microchannel, our acoustofluidic pump can generate a stable unidirectional flow (∼nanoliter per second flow rate) with a precise digital regulation (∼second response time), and it is capable of handling aqueous solutions (e.g., PBS buffer) as well as high viscosity liquids (e.g., human blood) with a nanoliter-scale volume. Along with our acoustofluidic pump's low cost, programmability, and capacity to control small-volumes at high precision, it could be widely used for point-of-care diagnostics, precise drug delivery, and fundamental biomedical research.
Article
Along with the considerable potential and increasing demand of the point-of-care testing (POCT), corresponding detection platforms have attracted great interest in both academic and practical fields. The first few generations of conventional detection devices tend to be costly, complicated to operate and hard to move on account of early limitations in the level of technological development and relatively high requirement of performance. Owing to the requirements for rapidity, simplicity, accuracy and cost controlling in the POCT, reader systems are urgently needed to be developed, upgraded and modified constantly, realizing on-site testing and healthcare management without a specific place or cumbersome operation. Accordingly, numerous rapid detection platforms with diverse size and performance have emerged such as bench-top apparatuses, handheld devices and intelligent detection devices. This review discusses various devices developed mainly for the detection of lateral flow test strips (LFTSs) or microfluidic strips in the POCT and summarizes these devices by size and portability. Furthermore, on the basis of various detection methods and diverse probes usually containing specific nanoparticles composites, three most common aspects of detection rationale in the POCT are selected to elaborate each kind of detection platforms in this paper: colorimetric assay, luminescent detection and magnetic signal detection. Herein, we focus on their structures, detection mechanisms and assay results, accompany with discussions and comments on the performances, costs and potential application, as well as advantages and limitations of each technique. In addition, perspectives on the future advances of detection platforms and some conclusions are proposed.
Article
We present and demonstrate a dextrous microfluidic device which features a reaction chamber with volume flexibility. This feature is critical for developing protocols directly on the chip when the exact reaction is not yet defined, enabling bio/chemical reactions on chip to be performed without volumetric restrictions. This is achieved by the integration of single layer valves (for reagent dispensing) and surface acoustic wave excitation (for rapid reagent mixing). We show that a single layer valve can control the delivery of fluid into, an initially air-filled, mixing chamber. This chamber arrangement offers flexibility in the relative volume of reagents used, and so offers the capability to not only conduct but also develop protocols on a chip. To enable this potential, we have integrated a SAW-based mixer into the system, and characterised its mixing time based on the frequency and power of excitation. Numerical simulations of the streaming pattern inside the chamber were conducted to probe the underlying physics of the experimental system. To demonstrate the on-chip protocol capability, the system was utilised to perform protein crystallization. Furthermore, the effect of rapid mixing, results in a significant increase in crystal size uniformity.
Article
This paper presents the design and development of a dual-chamber microchannel chip, coupled with an electromagnetic actuator for a bidirectional flow micropump system. A rapid prototyping technique is reported for the fabrication of the membrane sheet (a spin coater machine technique), microchannel chip (a photolithography technique) and controller system (a wet etching method to the circuit board), decreased development time by allowing correction and evaluation of the micropump to be made early in the process. To achieve a bidirectional flow, a dispersing depth was implemented between the microchannel chamber and inlet/outlet channel. From the numerical simulation and experimental analysis obtained, the micropump was capable for bidirectional flow application with the maximum volumetric flow rate of the fabricated micropump system at zero backpressure is 1.1254 ± 0.0658 μLs⁻¹ (forward direction) and 1.1266 ± 0.0760 μLs⁻¹ (reversed direction). The power consumption for the developed micropump system is 48.64 mW.
Article
This paper presents a review of the current state-of-the-art in micropumping technology for biomedical applications. The review focuses particularly on the actuation schemes, flow directing methods and liquid chamber configurations used in the devices proposed over the past five years. A comparative study is presented of the various mechanical and non-mechanical micropumps proposed for biomedical applications. The performance of the various devices is compared in terms of their actuation voltage, power consumption, operating frequency range, flow rate, backpressure, and so forth. The basic operating principles and advantages of each method are introduced, and their limitations described where appropriate. The review provides a useful source of reference for selecting micropumping schemes capable of meeting the specific flow rate requirements of different biomedical applications. In general, the review is expected to be of interest to both seasoned researchers and practitioners in the micropumping and biomedical technology fields and those entering the field for the first time.
Article
We have designed a pumpless acoustofluidic device for the concentration and separation of different sized particles inside a sin-gle-layered straight polydimethylsiloxane (PDMS) microfluidic channel. The proposed device comprises two parallel interdigi-tated transducers (IDTs) positioned underneath the PDMS microchannel. The IDTs produce high-frequency surface acoustic waves that generate semipermeable virtual acoustic radiation force field walls that selectively trap and concentrate larger particles at different locations inside the microchannel and allow the smaller particles to pass through the acoustic filter. The performance of the acoustofluidic device was first characterized by injecting into the microchannel a uniform flow of suspended 9.9 µm diam-eter particles with various initial concentrations (as low as 10 particles/mL) using a syringe pump. The particles were trapped with ~100% efficiency by a single IDT actuated at 73 MHz. The acoustofluidic platform was used to demonstrate the pumpless separation of 12.0 µm, 4.8 µm, and 2.1 µm microparticles by trapping the 12 µm and 4.8 µm particles using the two IDTs actuat-ed at 73 MHz and 140 MHz, respectively. However, most of the 2.1 µm particles flowed over the IDTs unaffected. The acousto-fluidic device was capable of rapidly processing a large volume of sample fluid pumped through the microchannel using an ex-ternal syringe pump. A small volume of the sample fluid was processed through the device using a capillary flow and a hydrody-namic pressure difference that did not require an external pumping device.
Article
Microfluidic systems enable rapid diagnosis, screening and monitoring of diseases and health conditions using small amounts of biological samples and reagents. Despite these remarkable features, conventional microfluidic systems rely on bulky expensive external equipment, which hinders their utility as powerful analysis tools outside of research laboratories. 'Self-contained' microfluidic systems, which contain all necessary components to facilitate a complete assay, have been developed to address this limitation. In this review, we provide an in-depth overview of self-contained microfluidic systems. We categorise these systems based on their operating mechanisms into three major groups: passive, hand-powered and active. Several examples are provided to discuss the structure, capabilities and shortcomings of each group. In particular, we discuss the self-contained microfluidic systems enabled by active mechanisms, due to their unique capability for running multi-step and highly controllable diagnostic assays. Integration of self-contained microfluidic systems with the image acquisition and processing capabilities of smartphones, especially those equipped with accessory optical components, enables highly sensitive and quantitative assays, which are discussed. Finally, the future trends and possible solutions to expand the versatility of self-contained, stand-alone microfluidic platforms are outlined.
Article
Foodborne illnesses have always been a serious problem that threats public health, so it is necessary to develop a method that can detect the pathogens rapidly and sensitively. In this study, we designed a magnetic controlled microfluidic device which integrated the dynamic magnetophoretic separation and stationary magnetic trap together for sensitive and selective detection of Salmonella typhimurium (S. typhimurium). Coupled with immunomagnetic nanospheres (IMNs), this device could separate and enrich the target pathogens and realize the sensitive detection of target pathogens on chip. Based on the principle of sandwich immunoassays, the trapped target pathogens identified by streptavidin modified QDs (SA-QDs) were detected under an inverted fluorescence microscopy. A linear range was exhibited at the concentration from 1.0×10(4) to 1.0×10(6)colony-forming units/mL (CFU/mL), the limit of detection (LOD) was as low as 5.4×10(3)CFU/mL in milk (considering the sample volume, the absolute detection limit corresponded to 540CFU). Compared with the device with stationary magnetic trap alone, the integrated device enhanced anti-interference ability and increased detection sensitivity through dynamic magnetophoretic separation, and made the detection in complex samples more accurate. In addition, it had excellent specificity and good reproducibility. The developed system provides a rapid, sensitive and accurate approach to detect pathogens in practice samples. Copyright © 2015 Elsevier B.V. All rights reserved.
Article
We present a microfluidic platform for simultaneous on-chip pumping and size-based separation of cells and particles without external fluidic control systems required for most existing platforms. The device utilizes an array of acoustically actuated air/liquid interfaces generated using dead-end side channels termed Lateral Cavity Acoustic Transducers (LCATs). The oscillating interfaces generate local streaming flow while the angle of the LCATs relative to the main channel generates a global bulk flow from the inlet to the outlet. The interaction of these two competing velocity fields (i.e. global bulk velocity vs. local streaming velocity) is responsible for the observed separation. It is shown that the separation of 5 μm and 10 μm polystyrene beads is dependent on the ratio of these two competing velocity fields. The experimental and simulation results suggest that particle trajectories based only on Stokes drag force cannot fully explain the separation behavior and that the impact of additional forces due to the oscillating flow field must be considered to determine the trajectory of the beads and ultimately the separation behavior of the device. To demonstrate an application of this separation platform with cellular components, smaller red blood cells (7.5 ± 0.8 μm) are separated from larger K562 cells (16.3 ± 2.0 μm) with viabilities comparable to those of controls based on a trypan blue exclusion assay.
Article
We have designed and characterized a surface acoustic wave (SAW) fluid actuation platform that significantly improves the transmission of sound energy from the SAW device into the fluid in order to obtain enhanced performance. This is in distinct contrast to previous SAW microfluidic devices where the SAW substrate is simply interfaced with a microchannel without due consideration given to the direction in which the sound energy is transmitted into the fluid, thus resulting in considerable reflective and dissipative losses due to reflection and absorption at the channel walls. For the first time, we therefore demonstrate the ability for continuous fluid transfer between independent reservoirs driven by the SAW in a miniature device and report the associated pressure-flow rate relationship, in which a maximum flow rate of 100 μl min(-1) and pressure of 15 Pa were obtained. The pumping efficiency is observed to increase with input power and, at peak performance, offers an order-of-magnitude improvement over that of existing SAW micropumps that have been reported to date.
Article
We might be at the turning point where research in microfluidics undertaken in academia and industrial research laboratories, and substantially sponsored by public grants, may provide a range of portable and networked diagnostic devices. In this Progress Report, an overview on microfluidic devices that may become the next generation of point-of-care (POC) diagnostics is provided. First, we describe gaps and opportunities in medical diagnostics and how microfluidics can address these gaps using the example of immunodiagnostics. Next, we conceptualize how different technologies are converging into working microfluidic POC diagnostics devices. Technologies are explained from the perspective of sample interaction with components of a device. Specifically, we detail materials, surface treatment, sample processing, microfluidic elements (such as valves, pumps, and mixers), receptors, and analytes in the light of various biosensing concepts. Finally, we discuss the integration of components into accurate and reliable devices.
Article
Immunoassays have greatly benefited from miniaturization in microfluidic systems. This review, which summarizes developments in microfluidics-based immunoassays since 2000, includes four sections, focusing on the configurations of immunoassays that have been implemented in microfluidics, the main fluid handling modalities that have been used for microfluidic immunoassays, multiplexed immunoassays in microfluidic platforms, and the emergence of label-free detection techniques. The field of microfluidic immunoassays is continuously improving and has great promise for the future.
Article
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.