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Particle Separation by Employing Non-UniformElectric Fields, Traveling-Wave Electric Fields andInclined GravityMasanori Eguchi a c , Hiroko Imasato b c & Takeshi Yamakawa a ca Department of Brain Science and Engineering , Kyushu Institute of Technology , 2-4Hibikino , Wakamatsu-ku, Kitakyushu, Fukuoka , 808-0196 , Japanb University of Occupational and Environmental Health , 1-1 Iseigaoka , Yahata-nishi-ku, Kitakyushu, Fukuoka , 807-8555 , Japanc Fuzzy Logic Systems Institute , 680-41 Kawazu , Iizuka, Fukuoka , 820-0067 , JapanPublished online: 01 Mar 2013.

To cite this article: Masanori Eguchi , Hiroko Imasato & Takeshi Yamakawa (2012) Particle Separation by EmployingNon-Uniform Electric Fields, Traveling-Wave Electric Fields and Inclined Gravity, Intelligent Automation & SoftComputing, 18:2, 121-137, DOI: 10.1080/10798587.2008.10643231

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Intelligent Automation and Soft Computing, Vol. 18, No. 2, pp. 121-137, 2012 Copyright © 2012, TSI® Press

Printed in the USA. All rights reserved

121

PARTICLE SEPARATION BY EMPLOYING NON-UNIFORM

ELECTRIC FIELDS, TRAVELING-WAVE ELECTRIC FIELDS AND INCLINED GRAVITY

MASANORI EGUCHI 1,3 , HIROKO IMASATO 2,3 AND TAKESHI YAMAKAWA 1,3

1Department of Brain Science and Engineering Kyushu Institute of Technology

2-4 Hibikino, Wakamatsu-ku, Kitakyushu, Fukuoka 808-0196, Japan

2University of Occupational and Environmental Health 1-1 Iseigaoka, Yahata-nishi-ku, Kitakyushu, Fukuoka, 807-8555, Japan

3Fuzzy Logic Systems Institute

680-41 Kawazu, Iizuka, Fukuoka 820-0067, Japan

ABSTRACT—In this study, we present the methods of the particle separation by employing electrokinetic phenomena (dielectrophoresis (DEP) and traveling-wave electroosmosis (TWEO)) and the inclined gravity. The methods can separate particles of same sign DEP. However, it is very difficult to separate particles on a plane electrode. To cope with this problem, we create the “Bottle neck Fork-trace electrode (BF electrode)” for separation of all particles in the chamber. Polystyrene beads, glass beads, yeast cells and barium titanate beads in NaCl solutions were separated by this electrode. Key Words: Dielectrophoresis, traveling-wave electroosmosis, ceiling electrode, inclined gravity, Bottle neck Fork-trace electrode (BF electrode).

1. INTRODUCTION In recent years, separation of micro particles, such as biological cells and virus has become a

crucial technology in the clinical laboratory. The centrifugation is commonly used for separation of different kinds of biological cells. However, this method is very difficult to separate the cells accurately, and require a fair amount of time. Other useful techniques are Fluorescence Activated Cell Sorting (FACS) and Magnetic Activated Cell Sorting (MACS). FACS and MACS are separating methods based on antigen-antibody reaction. Although these methods are efficient and fast, it is possible that some properties of cells will change during the labeling.

Dielectrophoresis (DEP) has attracted much interest because it is an effective label-free method (enables noninvasive) to manipulate and the separate particles such as living cells, viruses, DNA, and biomolecules [1-3]. The basic theory and application were suggested by Pohl [4]. DEP is a movement of particles in a given medium by a force, which is generated in a non-uniform electric field [4-6]. The particles move toward or away from a region of higher electric field. The dielectrophoretic force (DEP force) depends on the dielectric properties of particles and medium, radii of particles, and the electric field. TWEO is the fluid motion produced by the interaction of induced charge in the double layer (at the electrode/solution interface) with electric fields [7,8].

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122 Intelligent Automation and Soft Computing

TWEO is a unidirectional fluid motion induced by a traveling-wave electric field. Therefore particles are moved by a propulsion force, which is affected by the traveling-wave electroosmotic fluid flow.

In this paper, firstly, we present the methods of the particle separation by employing DEP, TWEO and the inclined gravity [9,10], the magnitude of which can be control by changing the angle of the inclined floor. The methods can separate particles of same sign DEP. However, it is very difficult to separate the particles on a plane electrode. To cope with this problem, we create the “Bottle neck Fork-trace electrode (BF electrode)” to separation of all particles in a chamber. The BF electrode is combined with the traveling-wave electrode array which induces TWEO, and the creek-gap electrode which induces DEP. The BF electrode is possible to transport all particles from the entire chamber to the electrode gap by TWEO at first, and then separate them by DEP and the inclined gravity. Polystyrene beads, glass beads, yeast cells and barium titanate beads in NaCl solutions are separated by this electrode.

2. THEORETICAL BACKGROUND

2.1 Dielectrophoresis (DEP) When a particle in medium is placed in an electric field E, an electric dipole moment p is

induced in the particle by the electric field. The dipole moment for a pair of opposite charges of magnitude q is defined as the charge magnitude multiplied by the distance between them. The direction of the dipole moment is toward the positive charge from the negative one. In a uniform electric field, the particle experiences equal opposing forces and the net force is zero (Figure 1(a)). On the other hand, in a non-uniform electric field, the net force is not zero because of the additive components (Figure 1(b)). This net force, i.e. so-called the dielectrophoretic force (DEP force), is given by the following equation [4-6];

[ ] 2*3 Re2 rmsCMmDEP Fεrπ EF ∇= (1)

where r is the radius of the particle, εm the permittivity of the medium, Re[FCM*] the real part of

the Clausius-Mossotti factor, and Erms the root-mean-square value of the electric field. The term 2

rmsE∇ is determined by the electrode shape and the applied voltage. The Clausius-Mossotti factor is given by

**

**

2 mp

mpCM εε

εεF

+−

= (2)

where εp* and εm

* are the complex permittivity of the particles and the medium, respectively, and are given by the following form;

ωσjεε −=* (3)

where σ is the conductivity, and ω the angular frequency. The magnitude of the DEP force depends on the permittivity of the medium, radius of the particle, and the electric field together with Re[FCM

*]. The polarity of the DEP force is determined by Re[FCM*], which depends on the

frequency. Figure 2 shows the dependency of Re[FCM*]. The Re[FCM

*] value changes from positive to negative according to the frequency as shown in Figure 2 (a) and (b). In the low frequency, Re[FCM

*] reaches the limiting value (σp - σm) / (σp + 2σm) which is determined only by the conductivities of the particle and the medium, without the permittivities. In the high frequency,

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Particle Separation by Employing Non-uniform Electric Fields, Traveling-Wave Electric Fields and Inclined Gravity 123

Re[FCM*] reaches the limiting value (εp - εm) / (εp + 2εm) which is determined only by the

permittivities of the particle and the medium, without the conductivities. When Re[FCM*] > 0, the

particle moves toward the region of higher electric field (“positive DEP”). When Re[FCM*] < 0,

the particle does the region of lower electric field (“negative DEP”). Consequently, the practical direction of the particle movement is determined by both of Re[FCM

*] and the electrode shape. Frequency response Re[FCM

*] of a particle is determined by the structure and material of the particle itself. The particle is assumed to be uniform in structure and material so far, for instance, polystyrene beads and glass beads. However, the biological cells exhibit the shell structure or the nuclear structure, for instance, a red blood cell (erythrocyte) or a white blood cell (leukocyte), respectively. The frequency response Re[FCM

*] of these cells is analyzed through the concentric multi-shell model [1,11].

(a) (b)

Figure 1. Particle in an electric field. (a) Uniform electric field. (b) Non-uniform electric field.

(a) (b)

Figure 2. Frequency response of the real part of Clausius-Mossotti factor for a homogeneous particle. (a) εp = 3ε0 (ε0 = 8.854×10-12 F/m), εm = 80ε0, σp = 10 mS/m, σm = 2 mS/m. (b) εp = 80ε0, εm = 3ε0, σp = 2 mS/m, σm = 10 mS/m.

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2.2 Traveling-Wave Electroosmosis (TWEO) Traveling-wave dielectrophoresis (TWD) induced by a traveling-wave electric field is

suitable for transporting and separating particles such as blood cells, yeast cells, and cancer cells [12-14]. Masuda et al. proposed the separation of small particles using the traveling-wave electric field [15] and demonstrated the controlled translational motion of red blood cells [12]. Figure 3 shows the typical geometry of a traveling-wave electrode array. The phase shifts between the voltages applied to next-neighbor electrodes are 90 degrees. In the traveling-wave electric field, the particles are moved by TWD force at right angle with electrode. The direction of TWD force depends on the dielectric properties of the particle and the medium. The traveling-wave electrode array is also used to induce traveling-wave electroosmotic (TWEO) fluid flow [7,8]. TWEO is the fluid flow produced by the interaction between the electric field and induced charge in the double layer (at the electrode/solution interface). TWEO is a unidirectional fluid flow induced by the traveling-wave electric field. Therefore the particles are moved by a propulsion force, which is affected by the traveling-wave electroosmotic flow (TWEO flow). Experimental discrimination between TWD and TWEO is very difficult, if not impossible. The propulsion force in the low voltage and low frequency range seems to be dominated by the TWEO flow. At the surface of the electrode, the TWEO flow is driven in the same direction as traveling-wave. In closed microsystem, the fluid recirculates above the electrode. The particles are moved by a propulsion force, which is affected by the TWEO flow. The propulsion force depends on the frequency, the applied voltage.

Figure 3. The schematic of the traveling-wave electrode array.

2.3 Flooring Electrode and Ceiling Electrode The thin-film electrode is formed on the floor of the DEP device in ordinary case (Figure

4(a)). When AC voltage is applied to the electrode, the electric field focuses at the edge of the electrode. In this case, it is difficult to separate the particles which exhibit positive DEP, because the particles are trapped at the edge of the electrode. To cope with this problem, we arranged the electrode on the ceiling of the chamber to avoid the trap of the particles, with the gravitational force FG, at the edge of the electrode (Figure 4(b)). We call this placement of the electrode “ceiling electrode” [16]. The positive DEP force experienced by a particle (diameter = 10 μm) under the ceiling electrode is illustrated in the following. Figure 5 shows the distribution of direction and intensity of the electric field, where they are represented by the direction and the length of arrows. Considering the horizontal behavior of a particle at the height of the particle

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(a-1) (a-2)

(b-1) (b-2)

Figure 4. Electrode placement of the DEP device. (a) Flooring electrode. (b) Ceiling electrode.

Figure 5. The electric field in case of the ceiling electrode.

center (height = 5 μm), the electric field just under the middle point of the electrode gap is much higher than other points. Thus, the horizontal component of the positive DEP force FDEP_x is generated on the particle, the direction of which is from the point of lower electric field to the higher one (Figure 4(b-1)). Therefore, the particle moves to the point of higher electric field, i.e. the middle point of the electrode gap, by the horizontal positive DEP force. On the other hand, considering the vertical behavior of the particle at any points, the magnitude of the electric field increases as the point approaches the height of electrode. The vertical component of the positive DEP force FDEP_y is generated on the particle, the direction of which is upward (Figure 4(b-1)). Consequently, when gravitational force of the particle FG > FDEP_y, the particles are not trapped at the edge of the ceiling electrode and they are moved by the positive DEP force to the narrow of the gap on the floor of the chamber (Figure 4(b-2)). FG is given by

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gF )(34 3

mpG ρρrπ −= (4)

where r is the radius of the particle, ρp the mass density of the particle, ρm the mass density of the medium, g the gravitational acceleration.

2.4 Inclined Gravity The particle separation with the DEP force is very difficult for the particles of same sign DEP.

To cope with this problem, we employed the “inclined gravity” to separate the particles of same sign DEP. The inclined gravity has been developed for measuring the DEP force [9,10].

When the device is set up on the inclined floor environment (see Figure 6), the DEP force (FDEP) is upward along the floor inclined at a degree θ. The Inclined gravity (FG(θ)) on the particle is the component of the gravitational force which acts oppositely to the DEP force and given by the following equation;

θρρrπθ mpG sin)(34)( 3 gF −= (5)

where r is the radius of the particle, ρp the mass density of the particle, ρm the mass density of the medium, g the gravitational acceleration. It is possible to adjust the inclined gravity by changing the angle θ. In the null method, the difference between the DEP force FDEP and the inclined gravity FG(θ) is adjusted to be zero. If these two forces are balanced, the particle movement comes to stop and the DEP force FDEP can be calculated by the following equation if ρp , ρm, and r are known and θ is measured.

θρρπθ sin)(34)( 3 gFF mpGDEP r −== (6)

Figure 7 shows a photograph of the measuring system which has function of adjusting θ. The immovability of particles was observed using the digital microscope (Digital Microscope VHX-200, Keyence).

Figure 6. The separation method of particles by Employing DEP force and Inclined gravity.

Figure 7. The photograph of measuring system.

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3. PARTICLE SEPARATION BY DIELECTROPHOREDSIS (DEP) OR TRAVELING-WAVE ELECTROOSMOSIS (TWEO) WITH A FLOORING/CEILING ELECTRODE UNDER THE INCLINED GRAVITY

3.1 DEP Device The DEP device presented in this paper consists of a pair of electrodes which is fabricated by

micro-fabrication technology and generates the DEP force by non-uniform electric field. The dielectrophoretic behavior of particles or biological cells can be observed under the microscope through a transparent window of the DEP device. The structure of the DEP device is shown in Figure 8. The electrode material is aluminum or Indium Tin Oxide (ITO). The device consisted of a slide glass, a cover glass and a silicon rubber (50 μm in thickness) to construct a thin chamber which is filled with micro-particle suspension. We proposed the “creek-gap electrode” the shape of which looks like a creek and generate the specific profile of the DEP force [9,10]. The creek-gap electrode has two equilibrium points where FDEP = FG(θ) (Figure 9). Therefore, it is possible to measure both of the positive and negative DEP forces [9,16]. The creek-gap electrode is employed in the DEP device. Figure 8(a) shows the DEP device of the creek-gap electrode formed on the floor of the chamber (“flooring creek-gap electrode”). The flooring creek-gap electrode is employed to separate particles of negative DEP (section 3.2). Figure 8(b) shows the DEP device of the “ceiling creek-gap electrode” which is employed to separate particles of positive DEP (section 3.3).

(a) (b)

Figure 8. The schematic view of the DEP device. (a) The creek-gap electrode formed on the floor of the chamber (flooring creek-gap electrode). (b) The creek-gap electrode formed on floor of the chamber (ceiling creek-gap electrode).

3.2 Separation of Particles by Negative DEP Under the Inclined Gravity The flooring creek-gap electrode (Figure 8(a)) is used for separation of particles of negative

DEP in this experiment. Polystyrene beads (mass density = 1.06, diameter ≈ 24 μm, Duke Scientific) and glass beads (mass density = 2.55, diameter ≈ 10 μm, Duke Scientific) are suspended in 1mM NaCl solution (mass density = 1.00) containing surface-activating agent

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Figure 9. The schematic profile of the DEP force of the creek-gap electrode.

(0.5 % Tween 20, Tokyo Kasei Kogyo). Figure 10 shows a photo of separation of the two kinds of particles of negative DEP, i.e. small particles (glass beads) and big particles (polystyrene beads), at θ = 7 degrees when a voltage (14 Vpp, 1 MHz) was applied to the creek-gap electrode. The glass beads came to stop at the position where the gap of the electrodes is narrow, and the polystyrene beads came to stop at the position where the gap of the electrodes is wide.

Figure 10. Separation of the two kinds of negative DEP, i.e. small particles (glass beads) and big particles (polystyrene beads), at θ = 7 degrees when a voltage (14 Vpp, 1 MHz) was applied to the creek-gap electrode.

3.3 Separation of Particles by Positive DEP with a Ceiling Electrode Under the Inclined Gravity

The ceiling creek-gap electrode (Figure 8(b)) is employed for the separation of particles of positive DEP in this experiment. Yeast cells (mass density = 1.07, diameter≈ 5 μm) and barium titanate (BaTiO3) beads (mass density = 6, diameter≈ 10 μm, Nippon Chemical Industrial Co. Ltd, Japan) are suspended in 1mM NaCl solution (mass density of 1.00) containing surface-activating agent (0.5 % Tween 20, Tokyo Kasei Kogyo). Figure 11 shows a photo of the separation of the two kinds of particles of positive DEP. The yeast cells came to stop at the position where the gap of the electrodes is narrow. The BaTiO3 beads came to stop at the position where the gap of the electrodes is wide.

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Figure 11. Separation of the two kinds of particles of positive DEP at θ = 2 degrees when a voltage (13.5 Vpp, 80 MHz) was applied to the creek-gap electrode.

3.4 Separation of Particles by TWEO with a Ceiling Electrode Under the Inclined Gravity [17]

The traveling-wave electrode array is fabricated by photolithography to produce a multi-layer electrode structure on a slide glass. The width of electrodes and gaps between them are 8 μm and 12 μm, respectively. The electrode material is aluminum (about 0.5 μm in thickness). Figure 12 shows schematic view of the TWEO device for experiment. In this experiment, Polystyrene beads (mass density = 1.06, diameter≈ 9.9 μm, Duke Scientific) and glass beads (mass density = 2.55, diameter≈ 10 μm, Duke Scientific) are suspended in 1mM NaCl solution (mass density = 1.00) containing surface-activating agent (0.5 % Tween 20, Tokyo Kasei Kogyo). The electrode array is arranged on the ceiling of the chamber to avoid the trap of the particles.

Figure 12. The schematic view of the TWEO device.

3.4.1 Separation of the Particles Being of the Same Material but of Different Size In this experiment, the polystyrene beads of various diameters (9.9 μm, 24 μm and 50 μm) are

suspended in NaCl solution. Figure 13 shows the typical frequency response of the equilibrium angle θ for different size of polystyrene beads when a voltage (1.25 Vpp) was applied. The equilibrium angles θ of the three particles were different from each other. The Figure 14 shows a photo of the separation of polystyrene beads of different size. When the angle was set to the equilibrium angle of the particle of 24 μm in diameter, the particle of 50 μm in diameter moved along the direction of the inclined gravity and the particle of 9.9 μm in diameter moved along the direction of the propulsion force.

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Figure 13. The frequency response of the equilibrium angle for different size of polystyrene beads.

(a) (b) (c) Figure 14. The separation of polystyrene beads of different size at 55 degree when a voltage (1.6 Vpp, 40 kHz) was applied to the creek-gap electrode. (a) t = 0 sec. (b) t = 12 sec. (c) t = 24 sec.

3.4.2 Separation of the Particles Being of the Same Size but of Different Material In this experiment, polystyrene beads of 9.9 μm in diameter and glass beads of 10 μm in

diameter are suspended in NaCl solution. Figure 15 shows a photo of separation of the particles of different material. When the angle was adjusted to 15 degree, the polystyrene beads moved along the propulsion force and the glass beads moved along the inclined gravity.

4. SEPARATION OF ALL PARTICLES IN THE CHAMBER BY CONBINING DIELECTROPHORESIS (DEP) AND TRAVELING-WAVE ELECTROOSMOSIS (TWEO) WITH A FLOORING/CEILING ELECTRODE UNDER THE INCLINED GRAVITY

4.1 Bottle Neck Fork-Trace Electrode (BF Electrode) When particles are on a plane electrode, the particles do not experience the DEP force.

Because the electric field at surface of the plane electrode is zero. Thus it is necessary to transport all particles from the entire chamber to the electrode gap, where the separation of the particles can be done. The transportation of all particles to the electrode gap and separation of them can be

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(a) (b) (c)

Figure 15. The separation of the particles of different material at 15 degree when a voltage (1.6 Vpp, 40 kHz) was applied to the creek-gap electrode. (a) t = 0 sec. (b) t = 7 sec. (c) t = 14 sec.

achieved by combining the traveling-wave electrode array and the creek-gap electrode. We created the electrode, the structure of which is shown in Figure 16(a). A pair of electrode arrays for transportation of particles by TWEO is set up to construct the bottle neck with a clear field. The electrode array looks like the fork-trace which is a typical pattern of a Japanese stone garden. Thus we named this electrode “Bottle neck Fork-trace electrode (BF electrode)”. The BF electrode has the same profile of the DEP force on the central line of the clear field as the creek-gap electrode (Figure 16(b)).

(a) (b)

Figure 16. The Bottle neck Fork–trace electrode (BF electrode). (a) The photo of the BF electrode. (b) The profile of the DEP force on central line of clear field.

4.2 Application of Voltages for Transportation and Separation of Particles The BF electrode can induce TWEO and DEP according to the wiring of each electrode.

Figure 17 shows the wiring diagram of the BF electrode. When the BF electrode is wired as shown in Figure 17(a), the direction of the traveling-wave electric field is outward from the clear field. The particles above the BF electrode are moved by the propulsion force to the clear field (TWEO mode). When the BF electrode is wired as shown in Figure 17(b), the particles experience the DEP force in the clear field of the BF electrode (DEP mode).

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(a)

(b)

Figure 17. The schematic side view and the wiring diagram of BF electrode. (a) The wiring diagram of transportation of the particles by TWEO (TWEO mode). (b) The wiring diagram of separation of the particles by the DEP force and the inclined gravity (DEP mode).

4.3 Experiment Separating all Particles in the Chamber In this experiment, the two kinds of particles of negative DEP (polystyrene beads of 24 μm in

diameter, glass beads of 10 μm in diameter) and two kinds of particles of positive DEP (yeast cells of 5 μm in diameter, BaTiO3 beads of 10 μm in diameter) are suspended in 1mM NaCl solution containing surface-activating agent. The protocol separating all particles is shown in Figure 18. [Step 1] The wiring of the BF electrode is the TWEO mode and the BF electrode is flooring placement (Figure 18(a-1)). While all the particles of negative DEP (polystyrene beads and glass beads) are transported by TWEO (the propulsion force to clear field), those of positive DEP (yeast cells and BaTiO3 beads) are trapped at the edge of the electrodes. Therefore Figure 18(a-1) and (a-2) is dedicated to negative DEP. Figure 19 shows the photograph of transportation of all particles of negative DEP. The transportation of the polystyrene beads (big particle) and glass bead (small particles) was observed 70 second after four phase voltage application (3 Vpp, 100 kHz). [Step 2] The BF electrode is rewired for the DEP mode and the particles of negative DEP are separated by the negative DEP force and the inclined gravity (Figure 18(a-2)). Figure 20 shows the photograph of separation of all particles of negative DEP at °=7θ when a single phase voltage (10 Vpp, 1 MHz) was applied to the BF electrode. The glass beads came to stop at the position where the clear field is narrow, and the polystyrene beads came to stop at the position where the clear field is wide. [Step 3] The attitude of the device is turned over to reach the ceiling electrode and the BF electrode is rewired for the TWEO mode (Figure 18(b-1)). Figure 21 shows the photograph of the transportation of all particles of positive DEP. The transportation of the yeast cells (white and very small particles: difficult to recognize in the figure) and BaTiO3 beads (black and small particles) was observed 105 second after four phase voltage application (2 Vpp,100 kHz).

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(a-1) (b-1)

(a-2) (b-2)

Figure 18. The protocol separating all particles in the chamber. (a-1) Particle transportation of negative DEP by TWEO with flooring electrode (Step 1). (a-2) Particle separation by negative DEP with a flooring electrode under the inclined gravity (Step 2). (b-1) Particle transportation of positive DEP by TWEO with a ceiling electrode (Step 3). (b-2) Particle separation by positive DEP with a ceiling electrode under the inclined gravity (Step 4).

Figure 19. The photograph of the transportation of all particles of negative DEP when a four phase voltage (3 Vpp, 100 kHz) was applied to the BF electrode (Step 1).

[Step 4] The BF electrode is rewired for the DEP mode and the particles of positive DEP are separated by the positive DEP force under the inclined gravity (Figure 18(b-2)). Figure 22 shows the photograph of the separation of all particles of negative DEP at °=2θ when a single phase voltage (4 Vpp, 80 MHz) was applied to the BF electrode. The yeast cells (white particles) came to stop at the position where the clear field is narrow, and the BaTiO3 beads (black particles) came to stop at the position where the clear field is wide. The particles of negative DEP tumbled down, because the negative DEP force and the inclined gravity are additive and there is no equilibrium point.

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Figure 20. The photograph of the separation of all particles of negative DEP at θ = 7 degrees when a single phase voltage (10 Vpp, 1 MHz) was applied to the BF electrode (Step 2).

Figure 21. The photograph of the transportation of all particles of positive DEP when a four phase voltage (2 Vpp, 100 kHz) was applied to the BF electrode (Step 3). (a) t = 0 sec. (b) t = 50 sec. (c) t = 105 sec.

5. CONCLUSIONS In this paper, we created the “Bottle neck Fork-trace electrode (BF electrode)” to separate all

particles in a chamber. The BF electrode is combined with the traveling-wave electrode array which induces traveling-wave electroosmosis (TWEO), and the creek-gap electrode which induces dielectrophoresis (DEP). The BF electrode is possible to transport all particles from the entire chamber to the electrode gap by TWEO at first, and then separate them by DEP and inclined gravity, the magnitude of which can be control by changing the angle of the inclined

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Figure 22. The photograph of separation of the all particles of positive DEP at θ = 7 degrees when a single phase voltage (4 Vpp, 80 MHz) was applied to the BF electrode (Step 4).

floor. The polystyrene beads, the glass beads, the yeast cells and the barium titanate beads in the NaCl solutions were separated by employing the BF electrode. This method of particle separation by the BF electrode was based on the following three methods of separation and we presented them. (1) Separation of particles by negative DEP with a flooring electrode under the inclined gravity. (2) Separation of particles by positive DEP with a ceiling electrode under the inclined gravity. (3) Separation of particles by TWEO with a ceiling electrode under the inclined gravity.

ACKNOWLEDGEMENT This work was supported in part by a Grant-in-Aid for Specially Promoted Research (Project

No.20001008) granted in 2008 to Kyushu Institute of Technology, Yamaguchi University and Shizuoka University by Japan Ministry of Education, Culture, Sports, Science and Technology.

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4. H.A. Pohl, “Dielectrophoresis”, Cambridge University Press, New York, 1978. 5. T.B. Jones, “Electromechanics of Particles”, Cambridge University Press, New York, 1995. 6. H. Morgan and N.G. Green, “AC Electrokinetics: Colloids and Nanoparticles”, Research

Studies Press LTD., 2003. 7. B.P. Cahill, L.J. Heyderman, J. Gobrecht, and A. Stemmer, “Electro-Osmotic Streaming on

Application of Traveling-Wave Electric Field”, Physical Review E, Vol. 70, 036305, 2004. 8. A. Ramos, H. Morgan, N.G. Green, A. Gonzáles, and A. Castellanos, “Pumping of Liquid

with Traveling-Wave Electroosmosis”, Journal of Applied Physics, Vol. 97, 084906, 2005. 9. H. Imasato and T. Yamakawa, “Measurement of dielectrophoretic force by employing

controllable gravitational force”, Journal of Elecrtrophoresis, Vol. 52, pp. 1-8, 2008. 10. H. Imasato and T. Yamakawa, “Study on the Transient Response of Dielectrophoresis

Force in the Creek-Gap Electrodes (in Japanese)”, Proceedings of the 21st Bioengineering Conference and Annual Meeting of BED/JSME, Sapporo, January 23-24, pp. 373-374, 2009.

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ABOUT THE AUTHORS

M. Eguchi received his B. Eng. and M. Eng. degrees from Kyushu Institute of Technology, Japan in 2003 and 2006, respectively, where he is currently working toward his Ph.D. degree. His research interests include dielectrophoresis, traveling-wave electrokinetics and neural network.

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H. Imasato received her Ph. D degree in Department of Brain Science and Systems Engineering Kyushu Institute of Technology, Japan in 2008. From 1982, she had been a medical technologist at University hospital of Occupational and Environmental Health, Japan. From 2008, she had been a senior researcher at Fuzzy Logic Systems Institute. Her research interests dielectrophoresis and clinical laboratory test.

T. Yamakawa is now a special-appointment professor and a Professor Emeritus of Department of Brain Science and Engineering, Graduate School of Life Science and Systems Engineering, Kyushu Institute of Technology, Wakamatsu, Japan and also the chairman of Fuzzy Logic Systems Institute (FLSI). He received the B. Eng. degree in electronics engineering in 1969 from Kyushu Institute Technology, Tobata and the M. Eng. and Ph.D. degrees for his studies on electrochemical devices in 1971 and 1974, respectively, from

Tohoku University, Japan. He developed intrinsic fuzzy logic integrated circuits in pMOS (1983) and CMOS (1985), the fuzzy logic controller hardware (1986), the fuzzy logic computer hardware (1986), the fuzzy memory device (1986), fuzzy micro processors (rule chip and defuzzifier chip) (1988), the fuzzy neuron chip in BiCMOS technology (1991) and the chaos chip in CMOS technology (1992). His main research interest lies on hardware implementation of fuzzy systems, fuzzy neural networks, and chaotic systems, minimally invasive epileptic surgery, and application of dielectrophoresis to clinical laboratory automation. He holds more than 100 international and domestic patents. Prof. Yamakawa is a fellow of IEEE, International Fuzzy Systems Association (IFSA) and Japan Society of Fuzzy Theory and Systems (SOFT). He received IEEE 2008 Fuzzy Systems Pioneer Award. He is acting as a member of editorial board and a regional editor of 10 international professional journals. He contributed more than 80 international conferences as a member or the chairman of organizing/programming committee.

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particle separation by employing non-uniform electric fields, traveling-wave electric fields and...

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