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Depth Effects of
DEP Chip with
Microcavities
Array on
Impedance
Measurement for
Live and Dead
Cells
Cheng-Hsin Chuang - STUST
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Outline
• I. Introduction
• II. DEP theory
• III. Simulation
• IV. Fabrication and Measurement
• V. Conclusion
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I. Introduction
Electrical
detection
method
and
the
remarkable capability of positioning and
registration of cell with single-cell resolution
are concerned, nowadays.
- A DEP chip consisted of multilayer electrodes
and microcavities array for trapping cells and
further electrical measurement under singlecell level.
- Two kinds of cell lines, NB4 and HL-60 can be
clearly identified, and the effects of microcavity
on impedance measurement will be discussed
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by numerical simulation
and experimental data.
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II. DEP theory (1)
The time averaged dielectrophoretic force
acting on a spherical particle, immersed in a
medium and exposed to a spatially non-uniform
electric field can be described by. The dipole
component of the DEP force is
εm
is the electrical permittivity of the surrounding medium,
Rp
is the radius of the particle,
is the gradient of the square of applied electric field magnitude
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II. DEP theory (2)
For a dielectric uniform sphere, such as a bead,
it is given by
K (ω) is the frequency dependent ClaussiusMosotti (CM) factor, ε* is the complex
permittivity of the medium (m) or particle (p)
and defined by
where ε and σ are the permittivity and
conductivity of medium or particle, respectively,
and j is √(-1). Powerpoint Templates
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II. DEP theory (3)
> 0 it will induce positive-DEP
and the particle will move toward
the high intensity electric field
< 0 it will induce negative-DEP
and the particle will move toward
the low intensity electric field
So the direction of the DEP force is determined
by the CM factor, and the magnitude of the DEP
force is determined by the applied electric field
and the size of the particle.
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III. Simulation (1)
DEP Force Simulation
Fig. 1. (a) The contour of electric field for 10μm depth SU-8 microcavity, the
highest density of electric field is near middle electrode upon the SU-8 surface,
and the lowest value occurred at the bottom. (b) the density of electric field
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along the surface of SU-8 for the
different Templates
depths, 5, 10 and 15μm, respectively.
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III. Simulation (2)
DEP Force Simulation
Fig. 2. (a) The gradient of electric field intensity, 2E for 10μm depth SU-8
microcavity, the strongest DEP force happened near the top of SU-8
microcavity and move particle into microcavity by negative DEP (b) 2E along
the surface of SU-8 for different
microcavity
depths 5, 10 and 15μm,
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respectively.
II. Simulation (3)
DEP Force Simulation
Figure 3.
The
various
profiles of
2E for
different
distances
away from
the middle
electrode
surface,
such as 0,
2, 4 6, 10
and 28μm.
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III. Simulation (4)
Impedance Simulation
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III. Simulation (5)
Impedance Simulation
Figure 4. The total current density as impedance measurement by applied
voltage is 0.2V on a pair of bottom electrodes,
the frequency is 100kHz, and the depth of microcavity is 0μm;
(a) without particle in the SU-8 cavity; (b) the particle fixed in the SU-8 cavity.
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III. Simulation (6)
Impedance Simulation
Figure 5. The total current
density as impedance
measurement by applied
voltage is 0.2V on a pair of
bottom electrodes and the
scan frequency is form
1kHz to 3MHz, the depth
of microcavity is 10μm;
(a) without particle in the
SU-8 cavity;
(b) the particle fixed in the
SU-8 cavity.
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IV. Fabrication and Measurement (1)
DEP Chip
Figure 6. The
microfabrication
processes of
multilayer
electrodes DEP
chip for
single-cell
level impedance
measurement
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IV. Fabrication and Measurement (2)
DEP Chip
Figure 7. SEM pictures of SU-8 cayitys array, the diameter and spacing are
both 16 m and the depth is 10 m, (a) 2 by 2 cavitys array; (b) Nanofocus
image for 5 m depth (c) The picture
of multilayer
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The blast diagram of DEP chip.
IV. Fabrication and Measurement (3)
DEP Chip
Figure 8. OM pictures of SU-8 microcavities array, the diameter and
spacing are both 16 m and the depth is 10 m; (a) the layout of four
individual impedance electrodes under four specific the microcavities; (b)
the gap of impedance electrode is 8 m.
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IV. Fabrication and Measurement (4)
Experimental setup
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IV. Fabrication and Measurement (6)
Capability of Trapping Cells
Figure 10. The optical micrographs show the capability of trapping HL-60
cell. (a)-(c) The HL-60 cell subjected to negative DEP effect and would be
attracted at the region of lower intensity of electric field by applied AC signal
with 10VPP and 10KHz; (d)-(f) the cells began move toward to the maximum
regions of electrical field intensity by positive DEP force as applied an AC
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signal with 10 Vpp and 500 KHz.
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IV. Fabrication and Measurement (7)
Impedance Measurement
Figure 11. The results of impedance measurement for the 5 m-depth
microcavity under four conditions: (1) only DI water without cells, (2) only
sucrose solution without cells, (3) HL60 live cell immersed in sucrose solution,
(4) HL60 dead cell immersed in sucrose solution, all conditions were applied
0.2V and the frequency range is 1K to 3M Hz. (a) impedance magnitude (ohm);
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(b) phase (degree).
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IV. Fabrication and Measurement (8)
Impedance Measurement
Figure 12. The results of impedance measurement for the 10 m-depth
microcavity under five conditions: (1) only DI water without cells, (2) only
sucrose solution without cells, (3) HL60 live cell immersed in sucrose solution,
(4) NB4 live cell immersed in sucrose solution,(5) NB4 dead cell immersed in
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sucrose solution, all conditions
were applied
0.2V and the frequency range is
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1K to 3M Hz. (a) impedance magnitude (ohm); (b) phase (degree).
V. Conclusions
We have designed and fabricated a DEP chip with
multilayer electrodes and microcavity array for
impedance measurement of single cell.
The depth effects on impedance difference were
analyzed by finite element method and verified
by experimental results.
This microchip not only provides an efficient way
to immobilization cells in the microcavity for a
long period of time without applying DEP force
but also easily identifies the live and dead cells
based on impedance
measurement
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