58
3. OPTO-ELECTRONIC INTEGRATION OF THICK-ELECTRODE DEP MICROFLUIDIC CHIP
caused by the cytoskeleton can be used to diagnose cancer. On the basis of the measurement of the
electrical properties of cells in the previous chapter, the addition of single-cell mechanical property
measurement can provide a more comprehensive and in-depth means for specicity analysis of
single cells.
3.2 PROGRESS IN SINGLECELL MECHANICAL PROPERTY
MEASUREMENT
e current main methods for measuring single-cell mechanical properties are as follows.
1. Magnetic twisting methods. In 1993, Wang et al. proposed the use of a non-de-
structive magnetic eld to drive a magnetic bead attached to the surface of a cell,
exerting a force on the cell, and recording the response of the cell structure under
force. e amount of deformation of the cells was calculated via the displacement of
the magnetic particles under the action of the magnetic moment, and the inuence
of the mechanical signals on the structure and function of the cells was quantitatively
measured in real time [178]. However, the magnetic properties of the cells can only
be tested by magnetic beads, and the results of the tests vary greatly depending on the
position of the magnetic beads on the cells [179].
2. Atomic force microscopy. Atomic force microscopy relies on the indentation changes
produced by the cantilever probe on the cells to measure the mechanical properties of
the cells. Atomic force microscopy method is generally suitable for the measurement
of adherent cells, but the location of the indentation on a single cell has a large eect
on the measurement of mechanical properties [180], as shown in Figure 3.1(a). e
measurement point reects the local mechanical properties of the cell at the 10 nm
level due to the probe size, and the throughput of the method is relatively low.
3. Micropipette aspiration methods. Mitchson et al. presented the micropipette aspi-
ration method in 1954, as shown in Figure 3.1(b) [181]. e micropipettes having
a diameter smaller than the cells are used to aspirate the cells. Under the action of
negative pressure, the cells are deformed into the micropipettes, and the mechanical
properties of the cells are measured by mapping the relationship between the defor-
mation and the negative pressure. In contrast to atomic force microscopy, micropi-
pette aspiration method is suitable for suspended cells and has been widely used in the
measurement of mechanical properties of various white blood cells [182]. However,
the results measured by this method are related to the size of the micropipette. e
closer the micropipette diameter is to the cell diameter, the better the whole mechan-
ical properties of the cell [183].
59
A
B
photodetector
cantilever deection (h)
laser
cell
probe
position (Z)
piezoelectric
actuator
(a) (b)
Figure 3.1: (a) Atomic force microscopy [180]; and (b) micropipette aspiration method [181], based
on and used with permission fromAIP Publishing.
4. Cell transit analyzers methods. Cell transit analyzers methods assess cellular me-
chanical properties by measuring the time the cells take to pass through a microchan-
nel [184, 185]. e advantage of the method is the ability to measure cellular mechan-
ical properties with high throughput, allowing nearly one second to test a cell [186].
To further increase throughput, Rosenbluth et al. proposed a microuidic chip that
simultaneously measures cellular mechanical properties in multiple channels, as
shown in Figure 3.2(a). Although the throughput of this method is higher than other
measurement methods, this method needs to consider the cell sizes, cell viscosities,
and the clogging problem [187].
A
B C
uch media
syringe pump
Optical Beam
OF OF
GUVS
cells
waste
(a) (b)
(a)
(b) (c)
Figure 3.2: (a) Measurement of cellular mechanical properties by cell perforation [187], based on and
used with permission from the Royal Society of Chemistry; and (b) dual-beam optical stretching
method [188], based on and used with permission from the Royal Society of Chemistry.
3.2 PROGRESS IN SINGLECELL MECHANICAL PROPERTY MEASUREMENT
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