Continuous separation of microparticles in aqueous medium by means of dielectrophoresis

There is a widespread need to separate microparticles suspended in liquid media. Dielectrophoresis (DEP), a technique for manipulating the motion trajectories of suspended particles, has enormous potential for solving difficult particle-particle separation problems. Nevertheless, the great majority of DEP applications have been limited so far to microchannels and lab-on-a-chip devices, with throughput typically in the A LA min-1 range. A promising, alternative solution to this problem is anticipated by upscaling DEP systems to enable high-throughput DEP separation on a clinical or industrial scale. To achieve this, a novel interdigitated electrode (IDE) design is proposed to meet the need for a high electric field when upscaling a DEP system. Numerical simulation using OpenFOAM demonstrated that, when replacing conventional plate IDE by cylindrical IDE (cIDE) in microchannel systems, the dielectrophoretic force field, represented by the gradient of the squared electric field, becomes stronger and more homogeneously distributed along the electrode array. The resulting particle DEP velocities were also higher for the cIDE. Simulations confirmed by experiments allow further predictions of particle motion in enlarged cIDE-DEP systems. Understanding how the interplay of channel geometry and electrode concept affects induced particle velocity is crucial when designing DEP separators having sufficiently high throughput to reach preparative scale. The objective of tailored design is to control particle motion trajectories predominantly by DEP while avoiding electrothermal interference in the form of fluid convection induced by a temperature gradient in the liquid phase due to Joule heating. One solution to this Joule heating problem in large-scale DEP systems is to tailor the ratios of electrode diameter, electrode distance and channel height. Based on model calculations, the influence on particle trajectories of both DEP force and drag force due to thermal convection was predicted for a case study involving a channel with rectangular cross section and an array of cIDEs at the bottom. The models were successfully verified by experimentally measuring and quantitatively analysing velocities of polyelectrolytic resin microparticles located at the subsurface of demineralized water. This allowed a qualitative sensitivity analysis of the impact of voltage input, particle size and medium properties on critical design parameters. From this, design criteria were deduced for the cIDE-DEP system that allow the influence of Joule heating to be minimised. There is still a need for continuous, contact-free fractionation of microparticles at high throughput. To achieve this, a sheath-flow-assisted dielectrophoretic continuous field-flow separator with a tailored arrangement of cIDE was developed, and size-dependent trajectories of dispersed particles were observed. Using a voltage input of 200 Veff at a frequency of 200 kHz, polystyrene particles (45, 25, and 11 Amicrometre in diameter) were levitated to different heights due to a negative DEP force. Experimental observations agree well with simulated particle trajectories that were obtained from by a modified Lagrangian particle tracking model in combination with Laplace's and Navier-Stokes equations. A theoretically calculated system throughput of up to 47 mLA min-1 was found to be possible by trading off design and operation parameters, enabling contact-free fractionation of sensitive microparticles with negligible shear stress. For further upscaling of the cIDE-DEP separation system, a new separation device with concentrically arranged cIDE configuration was proposed. Proof-of-concept is demonstrated by numerically predicting microparticle motion trajectories within the separator. Simulations show that a remarkable increment of suspension throughput can be achieved by the concentric cIDE separator compared to the cIDE separator under the same circumstances. From an evaluation of the impact of operating parameters on particle displacement, it can be deduced that continuous fractionation is possible even at system throughputs in the of hundreds of mLA min-1 range by using the concentric cIDE separator. These theoretical findings lay the foundation for continuous DEP-based microparticle separation on an industrial scale

Numerical modeling of dielectrophoretic effect for manipulation of bio-particles

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.This text describes different aspects of the design of a Doctor-on-a-Chip device. Doctor-on-a-Chip is a DNA analysis system integrated on a single chip, which should provide all of the advantages that stem from the system integration, such as small sample volume, fast and accurate analysis, and low cost. The text describes all of the steps of the on-chip sample analysis, including DNA extraction from the sample, purification, PCR amplification, novel dielectrophoretic sorting of the DNA molecules, and finally detection. The overview is given of the technologies which are available to make the integration on a single chip possible. The microfluidic technologies that are used to manipulate the sample and other chemical reagents are already known and in this text they are analyzed in terms of their feasibility in the on-chip system integration. These microfluidic technologies include, but are not limited to, microvalves, micromixers, micropumps, and chambers for PCR amplification. The novelty in the DNA analysis brought by Doctor-on-a-Chip is the way in which the different DNA molecules in the sample (for example, human and virus DNA) are sorted into different populations. This is done by means of dielectrophoresis – the force experienced by dielectric particles (such as DNA molecules) when subject to a non-uniform electric field. Different DNA molecules within a sample experience different dielectrophoretic forces within the same electric field, which makes their separation, and therefore detection, possible. In this text, the emphasis is put on numerical modelling of the dielectrophoretic effect on biological particles. The importance of numerical modelling lies in the fact that with the accurate model it is easier to design systems of microelectrodes for dielectrophoretic separation, and tune their sub-micrometre features to achieve the maximum separation efficacy. The numerical model described in this text is also experimentally verified with the novel microelectrodes design for dielectrophoretic separation, which is successfully used to separate the mixture of different particles in the micron and sub-micron range

Micromachines for Dielectrophoresis

An outstanding compilation that reflects the state-of-the art on Dielectrophoresis (DEP) in 2020. Contributions include: - A novel mathematical framework to analyze particle dynamics inside a circular arc microchannel using computational modeling. - A fundamental study of the passive focusing of particles in ratchet microchannels using direct-current DEP. - A novel molecular version of the Clausius-Mossotti factor that bridges the gap between theory and experiments in DEP of proteins. - The use of titanium electrodes to rapidly enrich T. brucei parasites towards a diagnostic assay. - Leveraging induced-charge electrophoresis (ICEP) to control the direction and speed of Janus particles. - An integrated device for the isolation, retrieval, and off-chip recovery of single cells. - Feasibility of using well-established CMOS processes to fabricate DEP devices. - The use of an exponential function to drive electrowetting displays to reduce flicker and improve the static display performance. - A novel waveform to drive electrophoretic displays with improved display quality and reduced flicker intensity. - Review of how combining electrode structures, single or multiple field magnitudes and/or frequencies, as well as variations in the media suspending the particles can improve the sensitivity of DEP-based particle separations. - Improvement of dielectrophoretic particle chromatography (DPC) of latex particles by exploiting differences in both their DEP mobility and their crossover frequencies

Design, test and biological validation of microfluidic systems for blood plasma separation

Sample preparation has been described as the weak link in microfluidics. In particular, plasma has to be extracted from whole blood for many analysis including protein analysis, cell-free DNA detection for prenatal diagnosis and transplant monitoring. The lack of suitable devices to perform the separation at the microscale means that Lab On Chip (LOC) modules cannot be fully operated without sample preparation in a full-scale laboratory. In order to address this issue, blood flow in microchannels has been studied, and red blood cells behaviours in different geometrical environments have been classified. Several designs have been subsequently proposed to exploit some natural properties of blood flow and extract pure plasma without disturbing the cells. Furthermore, a high-level modelling method was developed to predict the behaviour of passive microfluidic networks. Additionally, the technique proposed provides useful guidance over the use of systems in more complex external environments. Experimental results have shown that plasma could be separated from undiluted whole blood in 10μm width microchannels at a flow rate of 2mL/hr. Using slightly larger structures (20μm) suitable for mass-manufacturing, diluted blood can be separated with 100% purity efficiency at high flow rate. An extensive biological validation of the extracted plasma was carried out to demonstrate its quality. To this effect Polymerase Chain Reaction (PCR) was performed to amplify targeted human genomic sequence from cell-free DNA present in the plasma. Furthermore, the influence of the sample dilution and separation efficiency on the amplification was characterised. It was shown that the sample dilution does have an influence on the amplification of house-keeping gene, but that amplification can be achieved even on high diluted samples. Additionally amplification can also be obtained on plasma samples with a range of separation efficiencies from 100% to 84%. In particular, two main points have been demonstrated (i) the extraction of plasma using combination of constrictions and bifurcations, (ii) the biological validation of the extracted plasma

Label-free cell separation and sorting in microfluidic systems

Cell separation and sorting are essential steps in cell biology research and in many diagnostic and therapeutic methods. Recently, there has been interest in methods which avoid the use of biochemical labels; numerous intrinsic biomarkers have been explored to identify cells including size, electrical polarizability, and hydrodynamic properties. This review highlights microfluidic techniques used for label-free discrimination and fractionation of cell populations. Microfluidic systems have been adopted to precisely handle single cells and interface with other tools for biochemical analysis. We analyzed many of these techniques, detailing their mode of separation, while concentrating on recent developments and evaluating their prospects for application. Furthermore, this was done from a perspective where inertial effects are considered important and general performance metrics were proposed which would ease comparison of reported technologies. Lastly, we assess the current state of these technologies and suggest directions which may make them more accessible