Chapter 7:Applications of Dielectrophoresis in Microfluidics
24 Oct 2014-pp 192-223
TL;DR: The present chapter presents the basic theory of EK and DEP covering the fundamentals of electrode-based DEP and insulator- based DEP; followed by strategically selected examples of DEP studies in the areas of nanoanalytical, bioanalytical and biomedical applications.
Abstract: Microfluidics has revolutionised the manner in which many assessments are carried out. Miniaturisation offers attractive advantages over traditional bench-scale techniques: only small quantities of samples and reagents are required, higher resolution and sensitivity, improved level of integration, lower cost and much shorter processing times. Electrokinetic (EK) techniques have proved to be efficient and robust platforms able to perform complex manipulation of bioparticles for a wide variety of applications. Dielectrophoresis (DEP) is an increasingly popular EK technique successfully used in many studies, as demonstrated by more than 300 papers published every year since 2008. DEP is an EK transport mechanism caused by polarisation effects when a dielectric particle is exposed to a nonuniform electric field. DEP offers great flexibility and several operation modes. The present chapter presents the basic theory of EK and DEP covering the fundamentals of electrode-based DEP and insulator-based DEP; followed by strategically selected examples of DEP studies in the areas of nanoanalytical, bioanalytical and biomedical applications. It is expected that DEP will continue to grow at a fast pace as one of the leading microfluidics techniques for the analysis of biological samples.
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TL;DR: This study confirmed the reliability and efficiency of the tapered DEP microelectrodes in the process of selective detection and rapid manipulation at a higher efficiency rate than straight-cut microelectros, which is significant in DEP technology applications.
27 citations
TL;DR: It is demonstrated that differences in the particle’s surface charge can also be exploited by means of iDEP; and that distinct types of nanoparticles can be identified by their polarization and dielectrophoretic behavior.
Abstract: The analysis, separation, and enrichment of submicron particles are critical steps in many applications, ranging from bio-sensing to disease diagnostics. Microfluidic electrokinetic techniques, such as dielectrophoresis (DEP) have proved to be excellent platforms for assessment of submicron particles. DEP is the motion of polarizable particles under the presence of a non-uniform electric field. In this work, the polarization and dielectrophoretic behavior of polystyrene particles with diameters ranging for 100 nm to 1 μm were studied employing microchannels for insulator based DEP (iDEP) and low frequency (<1000 Hz) AC and DC electric potentials. In particular, the effects of particle surface charge, in terms of magnitude and type of functionalization, were examined. It was found that the magnitude of particle surface charge has a significant impact on the polarization and dielectrophoretic response of the particles, allowing for successful particle assessment. Traditionally, charge differences are exploited employing electrophoretic techniques and particle separation is achieved by differential migration. The present study demonstrates that differences in the particle’s surface charge can also be exploited by means of iDEP; and that distinct types of nanoparticles can be identified by their polarization and dielectrophoretic behavior. These findings open the possibility for iDEP to be employed as a technique for the analysis of submicron biological particles, where subtle differences in surface charge could allow for rapid particle identification and separation.
24 citations
Cites background from "Chapter 7:Applications of Dielectro..."
...Electroosmotic flow (EOF) is commonly used as a liquid and particle pumping mechanism due to the attractive advantage of requiring no mechanical parts, as this phenomenon exploits the electrical double layer (EDL) of the device substrate material [1]....
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...Dielectrophoresis (DEP) is a peculiar electric-field driven technique since it exploits particle polarization effects, not electrical charge, when particles are exposed to a non-uniform electric field [1]....
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TL;DR: A library with a novel parameter referred to as the electrokinetic equilibrium condition for each strain, which will allow for fast identification of the studied bacterial and yeast cells in Electrokinetic (EK) microfluidic devices is developed and validated.
Abstract: The rising concern over drug-resistant microorganisms has increased the need for rapid and portable detection systems. However, the traditional methods for the analysis of microorganisms can be both resource and time intensive. This contribution presents an alternative approach for the characterization of microorganisms using a microscale electrokinetic technique. The present study aims to develop and validate a library with a novel parameter referred to as the electrokinetic equilibrium condition for each strain, which will allow for fast identification of the studied bacterial and yeast cells in electrokinetic (EK) microfluidic devices. To create the library, experiments with six organisms of interest were conducted using insulator-based EK devices with circle-shaped posts. The organisms included one yeast strain, Saccharomyces cerevisiae; one salmonella strain, Salmonella enterica; two species from the same genus, Bacillus cereus and Bacillus subtilis; and two Escherichia coli strains. The results from these experiments were then analyzed with a mathematical model in COMSOL Multiphysics®, which yielded the electrokinetic equilibrium condition for each distinct strain. Lastly, to validate the applicability EK library, the COMSOL model was used to estimate the trapping conditions needed in a device with oval-shaped posts for each organism, and these values were then compared with experimentally obtained values. The results suggest the library can be used to estimate trapping voltages with a maximum relative error of 12%. While the proposed electrokinetic technique is still a novel approach and the analysis of additional microorganisms would be needed to expand the library, this contribution further supports the potential of microscale electrokinetics as a technique for the rapid and robust characterization of microbes.
23 citations
TL;DR: A non-electrolytic micro/nano electroporation (NEME) electrode surface, in which the metal electrodes are coated with a dielectric, is developed, which shows that in NEME Electroporation, the electric fields could induce electroporated and dielectrophoresis simultaneously.
Abstract: It was recently shown that electrolysis may play a substantial detrimental role in microfluidic electroporation. To overcome this problem, we have developed a non-electrolytic micro/nano electroporation (NEME) electrode surface, in which the metal electrodes are coated with a dielectric. A COMSOL based numerical scheme was used to simultaneously calculate the excitation frequency and dielectric material properties dependent electric field delivered across the dielectric, fluid flow, electroporation field and Clausius-Mossotti factor for yeast and E. coli cells flowing in a channel flow across a NEME surface. A two-layer model for yeast and a three-layer model for E. coli was used. The numerical analysis shows that in NEME electroporation, the electric fields could induce electroporation and dielectrophoresis simultaneously. The simultaneous occurrence of electroporation and dielectrophoresis gives rise to several interesting phenomena. For example, we found that a certain frequency exists for which an intact yeast cell is drawn to the NEME electrode, and once electroporated, the yeast cell is pushed back in the bulk fluid. The results suggest that developing electroporation technologies that combine, simultaneously, electroporation and dielectrophoresis could lead to new applications. Obviously, this is an early stage numerical study and much more theoretical and experimental research is needed.
20 citations
TL;DR: This is the first study on DEP chromatography to assess performance in terms of resolution and separation efficiency, demonstrating the unique potential of iDEP chromatography.
Abstract: The development of insulator-based dielectrophoresis chromatography is proposed here as a novel hybrid technique that capitalizes on the simplicity of insulator-based dielectrophoresis (iDEP) and the well-known chromatographic theory. Chromatographic parameters are employed to characterize dielectrophoretic separation of particles with particles being eluted from the system as enriched particle peaks. By varying the characteristics of the insulating posts, it was possible to manipulate the interactions of the particles with the insulating post array which acted as the stationary phase. The present work studied how the characteristics of the particles affected the particle retention. Different types of particles have distinct interactions with the post array; these interactions depend on particle properties (size, electrical charge, and polarizability). This work includes mathematical modeling with COMSOL and extensive experimentation. Particles ranging from 1 to 10 μm in diameter were tested for retention time and eluted as peaks in the iDEP chromatography devices. Separation results were reported in the form of dielectropherograms including the estimation of retention time (tR), separation efficiency (N/meter), and separation resolution (Rs). Two full separations were demonstrated: a separation by charge between two types of particles of similar size (~ 10 μm) with different electrical surface charges and a separation by size between 2- and 5-μm particles with similar surface charge (difference in ζP of 4 mV). The achieved separation resolutions were Rs = 1.8 and Rs = 3.5, respectively. This is the first study on DEP chromatography to assess performance in terms of resolution and separation efficiency, demonstrating the unique potential of iDEP chromatography.
19 citations