15
It can be known from Equation (1-12) that the rotational torque is related to the imaginary
part of the K
CM
coecient, to the composite permittivity of the solution and particle and the electrical
signal parameter. e positive and negative parts of Im[K
CM
] determine the direction of the DEP
torque. When the sign changes, the direction of the torque acting on the particles also changes.
1.3.2 DEP PARAMETER ANALYSIS
From Equations (1-10) and (1-12), it is known that DEP force and torque are related to size, elec-
trical parameters of particle, electrical parameters of solution, and electric eld.
a. DEP force is related to the non-uniformity of the electric eld, and the particles
are subjected to DEP force only in a non-uniform electric eld.
b. DEP force is related to the particle size. e larger the particle, the greater the
DEP force.
c. e direction of DEP force is related to the real part of K
CM
factor. When
Re[K
CM
]> 0, the DEP force is positive, that is, pDEP force, and the particle will
move to the region with a large electric eld gradient, when Re[K
CM
] < 0. e
DEP force is negative, that is, the nDEP force, and the particle will move to a
region with a small electric eld gradient.
d. e DEP torque is related to the non-uniformity of the applied electric eld; the
particle is subjected to DEP torque only in a rotational electric eld.
e. e strength of DEP torque is related to the particle size. e larger the particle,
the larger DEP torque.
f. e direction of DEP torque is determined by the imaginary part of the K
CM
fac-
tor. When the value of Im[K
CM
] changes positively and negatively, the direction
of rotation of the particle changes.
1.3.3 ADVANCES IN DEPBASED SINGLECELL MANIPULATION
With the development of MEMS technology, the application range of DEP technology has been
extensively expanded. Researchers have proposed various types of DEP microuidic chips that
can be applied to biological objects of dierent scales, ranging from manipulation of DNA [104],
viruses [105], bacteria [106, 107], cells [108, 109], particles [110], and even model organisms.
Single-cell analysis is important for life sciences, clinical diagnosis, and drug evaluation [125,
126]. Traditional cell analysis methods collect the response of cell populations and can’t accurately
detect the information of individual cells. Biologists have conrmed that even mutated genes car-
ried by CTCs derived from the same tumor are dierent [127]. In addition, a small number of cells
1.3 DEP MICRODLUIDIC CHIPS
16
1. INTRODUCTION
may have profound eects on cancer origin, progression, and therapeutic research [128]. erefore,
single-cell analysis techniques are essential, so the corresponding single-cell sample manipulation
is also critical to the analysis.
Among many techniques, DEP has been widely used in single-cell manipulation because of
its label-free, non-invasive and highly selective properties [129]. DEP is less harmful to cells, and
the viability of biological cells after DEP can be as high as 91.9% [130]. At present, DEP manip-
ulations on single cells can be mainly divided into single-cell capture [131], single-cell translation
[132], cell fusion [133], cell rotation [134], etc. For example, Wu et al. proposed a single-cell capture
chip with microelectrode arrays, in which two electrodes inside the well can generate pDEP force
to attract single cells into the wells (Figure 1.11(a)) [135]. Şen et al. proposed a single-cell capture
chip with 900 gourd-shaped microwell arrays (Figure 1.11(b)) [136]. e electrodes in the arrays
interact with the top ITO electrode to capture dierent types of single cells. en, the captured
cells are paired by nDEP force.
Gel et al. designed a microuidic chip for cell fusion (Figure 1.11(c)) [137]. e micro-
structure in the microchannel is used to change the electric eld distribution, and the cells are
captured on both sides of the microstructure, and then the pulse is used to realize the electric
fusion of the cells. In addition to the use of DEP force to capture single cells, single-cell rotation
can be achieved by using DEP torque. For example, Bahrieh et al. used four planar electrodes
to achieve single-cell rotation (Figure 1.11(d)) [138], by measuring cell rotation spectra after
treatment with dierent drugs, electrical parameters of single cells can be measured for the study
of the eects of drug on cells.
(a)
Separation Area
Cell Mixture
Buffer Medium
Cell Mixture
Trapping Area
Channel A
Channel B
Channel C
V
2
(t) = A cos(wt + 90˚)
V
4
(t) = A cos(wt + 270˚)
V
1
(t) = A cos(wt)
V
3
(t) = A cos(wt + 180˚)
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