9
netized, the magnetic eld will be enhanced, which can amplify the magnetic eld strength in the
micro-channel, strengthen the interaction between the modied CTC and the magnetic eld, and
successfully achieve the capture of four cancer cell lines, with capture eciency >97%.
Magnetic activated cell sorting methods can eciently manipulate the target cells, but the
sample needs to be modied, and the peripheral magnetic eld generating device is required for the
control, which is inconvenient for miniaturization and integration of the chip.
Glass Slide Micromagnet
Permanent Magnet
Red Blood Cell
Nanoparticle-labeled
CTCs
Inlet
Outlet
500 µ
m
(a) (b)
Figure 1.5: Ferromagnetic microuidic system for enrichment of CTC [85]; (a) schematic diagram of
chip operation; and (b) dimensional drawing of chip specic structure.
1.2.4 ACOUSTIC METHODS
Due to the advantages of non-contact operation, low-cost, high-controllability and high-biocom-
patibility, surface acoustic wave (SAW) has been widely used in cell separation [86, 87] and cell
localization [88]. Acoustic methods generally realize the micro-operation of cells by forming an
acoustic eld in the microchannel by the piezoelectric transducer. Under the action of the acoustic
radiation force the cells move to the position of the node (the position with the smallest amplitude)
or the anti-node (the position with the largest amplitude). Cells with dierent physical properties
such as sizes and densities are subject to acoustic radiation forces of dierent magnitudes and di-
rections. e acoustic eld distribution can be adjusted and controlled by changing the shape and
position of the piezoelectric transducer. For example, Li et al. proposed a microuidic chip based on
SAW method, which can separate high concentration of CTC cells (~100 cells/ml) from peripheral
blood (Figure 1.6(a)) [89]. In order to achieve single-cell sorting, Collins et al. proposed a focused
SAW method that uses a focused interdigital transducer (FIDTs) to generate a local acoustic eld
for single-cell manipulation (Figure 1.6(b)) [90].
Acoustic methods can control cells without labels and damage, but it depends on the shape
of the microchannel and dicult to separate cells of similar size and density.
1.2 SAMPLE MANIPULATION METHODS IN MICROFLUIDIC CHIPS
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