27
However, the spatial position of the cell is unstable, and the electric eld decays rap-
idly in the vertical direction.
(a) (b)
A
sin(w
1
t + 0˚) + Bsin(w
2
t + 0˚)
Asin(w
1
t + 180˚) + Bsin(w
2
t + 270˚)
Asin(w
1
t + 0˚) + Bsin(w
2
t + 180˚)
Asin(w
1
t + 180˚) + Bsin(w
2
t + 90˚)
0˚
90˚
180˚
270˚
x
z
y
1
2
3
4
Microscopic Image Capture System
Projector
Optical Image
ITO Glass
ITO Glass
Medium
Amorphous Silicon
This work (rotation about the pitch axis
Previous
Works
Figure 2.5: Single-cell rotation based on DEP: (a) single-cell rotation using octagonal planar elec-
trodes [165], based on and used with permission from the Royal Society of Chemistry; and (b) sin-
gle-cell rolling operation using light-induced DEP [166], based on and used with permission from
AIP Publishing.
In order to overcome the decay problem of electric eld, Han et al. designed two sets of upper
and lower planar electrodes. e octagonal electrodes ensure the stable positioning of the cells and
achieve stable rotation of the cells [165], as shown in Figure 2.5(a). Liang et al. used an optoelec-
tronic material to prepare virtual electrodes, and the distribution of electric eld was changed by
adjusting the position and shape of light [166], as shown in Figure 2.5(b). Cells at the edge of the
virtual electrodes are vertically rotated under the DEP torque, but the area of the vertical rotation
is limited to the boundary of the virtual electrodes.
In summary, a lot of methods base on dierent technologies can achieve cell rotation, and
have their own advantages and applications. However, most of the methods can only achieve
2D/1D cell rotation. Cell rotation based on DEP technology enables precise rotation control and
can be used for measurement of cellular electrical parameters. e work of this chapter focuses on
how to construct a thick-electrode DEP multi-electrode chip to realize the operation and analysis
of single-cell 3D rotation.
2.3 THICKELECTRODE MULTIELECTRODE CHIP DESIGN
2.3.1 PRINCIPLE AND DESIGN OF THICKELECTRODE MULTI
ELECTRODE CONSTRUCTION
Based on the theory of DEP, how to design the electrode structure to generate a 3D rotational
electric eld is the key to realizing 3D rotation. In our previous work, a microchip with four thick
2.3 THICKELECTRODE MULTIELECTRODE CHIP DESIGN
28
2. THICK-ELECTRODE DEP FOR SINGLE-CELL 3D ROTATION
electrodes and two transparent planar electrodes can successfully obtain single-cell 3D electro-ro-
tation [167]. However, the device is an open chip and prepared by a machining process. It has a
problem in loading single cells, and is suitable only for cells with large size such as bovine oocytes.
Moreover, the single-cell rotation is not stable, and the sinking problem easily occurs.
e use of thick electrodes in rotation applications has many advantages: (a) thick electrodes
can overcome the limitations of 2D planar electrodes that can’t achieve 3D rotation; (b) thick
electrodes can solve the shortcoming of the electric eld attenuation of the planar electrodes in the
vertical direction, greatly increasing the rotatable spatial region; and (c) the electric eld distribu-
tion of thick electrodes in the vertical direction is more uniform and the cell rotation is more stable,
which ensures the accuracy of the results for electrical measurements.
Figure 2.6 shows a schematic diagram of a thick-electrode multi-electrode DEP rotation
structure. e multi-electrode structure consists four thick electrodes and a bottom electrode which
form an open electrode chamber.
ick
Electrode
Bottom
Electrode
Cell
Figure 2.6: 3D rotation electrode chamber structure.
Rotational electric elds in horizontal and vertical direction are generated by applying
dierent electrical signal conguration on dierent electrodes. Applying signals with the same
amplitudes, the same frequencies but dierent phase shifts on four vertical electrodes can form a
horizontally rotational electric eld in the chamber. As shown in Figure 2.7(a), the cells are subject
to torque in a horizontally rotational electric eld. Applying signals with the same amplitudes, same
frequencies, but dierent phase shifts on the opposite two vertical thick and bottom electrodes, as
shown in Figure 2.7(b), can generate a vertical rotational electric eld in the chamber.
29
(a) (b)
Figure 2.7: Signal conguration for 3D rotation: (a) in-plane rotation and (b) out-of-plane rotation.
rough simulation, the electric eld in the chamber can rotate horizontally and vertically
under dierent electrical signal congurations. Figure 2.8(a) is a horizontal rotation simulation di-
agram. Applying signals with phase shift of 90° (Vp-p = 10 V, f = 1 MHz) on four thick electrodes
will form a horizontally rotational electric eld in the chamber. A cell can do in-plane rotation by
a clockwise DEP torque under the horizontally rotational electric eld. Figure 2.8(b) is a vertical
rotation simulation diagram. Applying signals with phase shift of 120° (Vp-p = 10 V, f = 1 MHz) on
two opposite thick electrodes and bottom electrode. A vertical rotational electric eld is formed in
the vertical direction; the cell is subjected to torque for out-of-plane rotation. Since the electrodes
are not completely symmetrically distributed in the vertical direction, the strengths of the vertical
rotational electric eld are not the same at dierent times in one cycle.
(a) (b)
(
(
)
)
(b
(b
)
)
Surface Voltage (V) Arrow: Electric eld (V/m) Surface Voltage (V) Arrow: Electric eld (V/m)
Figure 2.8: Simulation of a 3D rotational electric eld: (a) top view of the electrode chamber (in-plane
rotation); and (b) side view of the electrode chamber (out-of-plane rotation).
2.3 THICKELECTRODE MULTIELECTRODE CHIP DESIGN
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