10
1. INTRODUCTION
Sheath Flow
T
ilted IDTs
Sheath Flow
Sample
SAW
Waste Collection
CTCs
WBCs
(a) (b)
Figure 1.6: Surface acoustic wave microuidic chip for cell sorting: (a) symmetrical forked surface
acoustic wave cell sorting chip [89]; and (b) fFocused surface acoustic wave single-cell sorting chip
[90]. Used with permission from the Royal Society of Chemistry.
1.2.5 DEP METHODS
Because of its label-free, low damage, high eciency and easy operation, dielectrophoresis (DEP)
technologies have been widely used in cell capture [91, 92], cell fusion [93, 94], and cell sorting [95,
96]. Due to the dielectric properties of cells, they could be polarized under non-uniform electric
elds and formed electric dipoles, which are subjected to DEP forces or torques. In association with
the dierences in electrical properties of cells, DEP force or torque diers across cells under the
same electric eld. DEP methods can control the strength and direction of DEP force and torque
by changing electrical signal parameters (amplitude, frequency and phase). Song et al. proposed a
microuidic chip for sorting stem cells (Figure 1.7(a)) [97]. ere is an angle between the DEP
force generated by the parallel electrodes and the ow force. Under the action of DEP force and
ow force, dierent types of cells will have dierent oset distances at the exit, which can realize
sorting of dierent cells. e chip has a collection eciency of 92% for human mesenchymal stem
cells along with purity up to 84%.
As opposed to traditional DEP methods, insulating pillar structures in microchannel were
also designed to produce DEP eect called insulator-based DEP (iDEP) [98, 99]. e insulating
pillar structures change the electric eld distribution in the microchannel and can generate DEP
force at the edge of the insulating pillars. LaLonde et al. proposed a cell enrichment microuidic
chip based on iDEP, as shown in Figure 1.7(b) [100]. e chip successfully captured and enriched
yeast cells with capture eciency > 99%.
11
Gold Electrode
AC Field with Alternative on/o Control
Cell S
ample
Buer Solution
Lower Outlet Upper Outlet
Insulating Posts
4.15 mm
1 mm
9.40 mm
2
4
3
10.16 mm
0.34 mm
(a) (b)
O On OnO O On O On O On O
Figure 1.7: DEP microuidic chip for cell sorting: (a) parallel electrode DEP cell sorting chip [97]
(used with permission from the Royal Society of Chemistry; and (b) insulating DEP cell enrichment
chip [100] (used with permission from AIP Publishing).
e strength and direction of DEP force and torque are related to the cell, solution, and
electrical signal parameters. By adjusting electrical signal parameters, precise manipulation of single
cells and cell population can be achieved. As MEMS technologies advance, the electrodes in micro-
uidic chips can be made more sophisticated, extending from 2D planar electrodes to thick-elec-
trode structures. And the microuidic chip based on the DEP technology can be easily combined
with other various technologies to realize multifunctional operations.
e above sample manipulation mechanisms are summarized in Table 1.1.
Table 1.1: Biological control mechanisms in microuidic chips
Methods eory rougput Application
Fluidic Microstructures or microvalves in microchannels
are used to control microuidics to control the
biological control
High Cell capture,
separation
Optical e optical gradient well formed by a single
beam is used to capture and move single cells
Low Cell capture,
Translation, Sorting
Magnetic Cell surface antigens are combined with specic an-
tibodies attached to magnetic beads to manipulate
cells using an external magnetic eld
High Cell enrichment
Acoustic e micro-operation of cells is realized by the
acoustic eld formed in the microchannel by
piezoelectric transducer device
High Cell separation,
cell trap
DEP e polarization of cells are formed electric di-
pole under non-uniform electric eld, which is
subjected to DEP force or torque
High Sorting,Separation,
Electro-rotation
1.2 SAMPLE MANIPULATION METHODS IN MICROFLUIDIC CHIPS
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