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Superpositioned dielectrophoresis for enhanced trapping efficiency
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
KTH, School of Engineering Sciences (SCI), Mechanics.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
KTH, School of Engineering Sciences (SCI), Mechanics.ORCID iD: 0000-0003-3336-1462
2005 (English)In: Electrophoresis, ISSN 0173-0835, E-ISSN 1522-2683, Vol. 26, no 22, 4252-4259 p.Article in journal (Refereed) Published
Abstract [en]

One of the major applications for dielectrophoresis is selective trapping and fractionation of particles. If the surrounding medium is of low conductivity, the trapping force is high, but if the conductivity increases, the attraction decreases and may even become negative. However, high-conductivity media are essential when working with biological material such as living cells. In this paper, some basic calculations have been performed, and a model has been developed which employs both positive and negative dielectrophoresis in a channel with interdigitated electrodes. The finite element method was utilized to predict the trajectories of Escherichia coli bacteria in the superpositioned electrical fields. It is shown that a drastic improvement of trapping efficiency can be obtained in this way, when a high conductivity medium is employed.

Place, publisher, year, edition, pages
2005. Vol. 26, no 22, 4252-4259 p.
Keyword [en]
alternating current electrokinetics; dielectrophoresis; Escherichia coli; field superposition; trajectory analysis
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-5516DOI: 10.1002/elps.200500068ISI: 000233740900003Scopus ID: 2-s2.0-28244475356OAI: oai:DiVA.org:kth-5516DiVA: diva2:9908
Note
QC 20100820Available from: 2006-03-22 Created: 2006-03-22 Last updated: 2017-11-21Bibliographically approved
In thesis
1. New Concepts for Dielectrophoretic Separations and Dielectric Measurements of Bioparticles
Open this publication in new window or tab >>New Concepts for Dielectrophoretic Separations and Dielectric Measurements of Bioparticles
2006 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

This thesis presents two new concepts for separation of micro particles using dielectrophoresis, demonstrated by calculated examples, as well as a new method for obtaining dielectric data on living cells. The thesis is based on four papers.

Paper I describes how the trapping efficiency of micro particles may be significantly increased when superpositioned electric fields are employed in a high conductivity medium. Avoiding low conductivity media is important when working with living cells. Calculations were performed to predict trajectories of Escherichia coli bacteria in the system with superpositioned electric fields, and a model was developed which employed two arrays of interdigitated electrodes in a micro channel.

Paper II proposes a new concept for separation of micro particles, based on repetitive dielectrophoretic trapping and release in a flow system. Calculations show that the resolution increases as a direct function of the number of trap and release steps, and that a difference in size will have a larger influence on the separation than a difference in dielectrophoretic properties. Polystyrene beads in deionized water were used as a model, and calculations were performed to predict the particle behavior and the separation efficiency. It should be possible to separate particles with a size difference of 0.2 % by performing 200 trap-and-release steps. The enhanced separation power of multi step dielectrophoresis could have significant applications, not only for fractionation of particles with small differences in size, but also for measuring changes in surface conductivity.

Paper III presents a new calculation method for predicting dielectrophoretic motion of micro particles. The method is based on a soft sphere method often used in molecular dynamics. Results from the calculations are in good agreement with theoretical predictions as well as initial experimental results, showing that the method provides good efficiency and accuracy.

Paper IV describes a new method for measurements of conductivity of living bacteria. To obtain reliable conductivity values, it is important to handle the cells as gently as possible during the measurement process. A standard conductivity meter was used in combination with cross-flow filtration. In this way, repeated centrifugation and resuspension is avoided which otherwise may cause damage to the bacteria. The conductivity of Bacillus subtilis was determined to be 7000 μS/cm by means of the cross-flow filtration method, and the values differ from earlier published values by almost an order of a magnitude.

In addition to the work presented in the papers, some experimental dielectrophoresis work in chip-based systems was performed. The behavior of Escherichia coli and polystyrene beads at different voltages and frequencies were studied. Separation of beads with different sizes was achieved on an array of interdigitated electrodes. Using electrodes with a pointed shape, alignment in different directions, pearl-chain formation, rotation, and other dielectrophoretic motion of E. coli were observed.

Place, publisher, year, edition, pages
Stockholm: Kemi, 2006. 26 p.
National Category
Analytical Chemistry
Identifiers
urn:nbn:se:kth:diva-3894 (URN)91-7178-286-9 (ISBN)
Presentation
2006-03-27, Sal K2, Teknikringen 28, Stokcholm, 10:15
Opponent
Supervisors
Note
QC 20101108Available from: 2006-03-22 Created: 2006-03-22 Last updated: 2010-11-08Bibliographically approved
2. Modeling of dielectrophoresis in micro and nano systems
Open this publication in new window or tab >>Modeling of dielectrophoresis in micro and nano systems
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This thesis presents models and simulations of dielectrophoretic separation of micro and nano particles. The fluid dynamics involved and the dielectric properties of water inside single-walled carbon nanotube are studied as well.

Based on the effective dipole moment method, the particle dynamic model focuses on the translational motions of micro particles. The hydrodynamic force between the particles and the particle-particle electrostatic interactions are considered as well. By comparing the dimensionless parameters, the dominating force can be determined. Based on a simplified version of the particle dynamic model, two numerical simulations are carried out to predict the efficiency of dielectrophoretic separation of micro size particles. The first calculation suggests a strategy to improve the trapping efficiency of E.coli bacteria by applying superimposed AC electric fields. The second calculation discusses the concept of mobility and improves the separation rate of particles by a multi-step trapping-releasing dielectrophoresis strategy.

The model is extended down scale to calculate the separation of metallic and semiconducting single-walled carbon nanotubes by the modified effective dipole moment method for prolate ellipsoids. The steeply changed gradient of electric field results in the local joule heating therefore creates gradient of dielectric properties in the solution. As a result, certain pattern of fluid flow with a considerable strength is created and affects the motion of carbon nanotubes especially close to the electrode gap, which indicates that the so-called electrothermal flow should be considered in designing the experiment to separate single-walled carbon canotubes.

When the length scale of particles is comparable to that of the electrodes, the calculation of dielectrophoretic force by the effective dipole moment is considered not to be accurate since only the electric field in the center point is taken into account. Hence in the thesis a new method based on distributed induced charge is suggested. By approximating a straight slender body as a prolate ellipsoid, the electric field of multiple points along the centerline are all considered in the calculation and the interaction between particles could be concurrently taken care. This method is expected to be an improved method to calculate the dielectrophoretic force of rod-like virus, DNA, nanowires and carbon nanotubes.

The dielectric property of water confined in carbon nanotubes is expected to be dramatically different from that of bulk water. The thesis also contains a molecular dynamics study to reveal the difference also a dependence on the diameter of carbon nanotubes. The results show that along the axial direction, both the static permittivity and the relaxation time are larger than the isotropic bulk water, and in the cross-section plane it is opposite. When the radius of the carbon nanotubes increases, the properties of water inside become closer to the bulk water.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. vii, 46 p.
Series
Trita-MEK, ISSN 0348-467X ; 2008:05
Keyword
Dielectrophoresis, micro particle, molecular dynamics, single-walled carbon nanotubes, hydrodynamics, particle-particle interaction, superimposed, multi-step
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-4784 (URN)978-91-7415-008-7 (ISBN)
Public defence
2008-06-11, Sal D2, KTH, Lindstedtsvägen 5, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100820Available from: 2008-06-02 Created: 2008-06-02 Last updated: 2010-08-20Bibliographically approved
3. Numerical modeling of dielectrophoresis
Open this publication in new window or tab >>Numerical modeling of dielectrophoresis
2006 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

We investigate the dielectrophoretic separation of microparticles. Two different models are formulated in two characteristic time scales. The first model mainly accounts for the orientation behavior and rotational motion of non-spheric microparticles. The concept of effective charge is suggested to calculate the finite size non-spheric particles. It is combined with the fluid particle dynamics method to calculate hydrodynamic as well as dielectrophoretic forces and torques. The translational motion and the particle-particle interaction are calculated also, but they take much longer time to be observed due to the different time scales of the rotational and translational motions By viewing the particle as spheres, the second model focus on the translational motion of spheres. The hydrodynamic force between particles and particle-particle electrostatic interactions are also taken into account. We check the relative magnitude ratio between these forces in order to determine the importance of these forces. To predict and guide the design of experimental dielectrophoretic separation, two numerical applications are carried out. The first calculation suggests optimum patterns to improve the trapping efficiency of E.coli. cells by applying superimposed AC electric fields. The second calculation finds out the mobility and separation rate of particles which differs in size and electric properties by a multi-step trapping-releasing strategy.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. viii, 34 p.
Series
Trita-MEK, ISSN 0348-467X ; 2006:14
Keyword
dielectrophoresis, orientation of rotation, fluid particle dynamics, microparticle, molecular dynamics, hydrodynamics, particle-particle interaction, superimposed, mobility
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-4014 (URN)
Presentation
2006-06-06, Sal D3, KTH, Lindstedtsvägen 5, Stockholm, 13:00
Opponent
Supervisors
Note
QC 20101118Available from: 2006-06-01 Created: 2006-06-01 Last updated: 2010-11-18Bibliographically approved

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