Biomedical Engineering Reference
In-Depth Information
drug-induced NT2 cell differentiation correlated well with the depletion of a key stem-cell
self-renewal factor, OCT4.
Overall, the key advantage of ECIS over conventional assays is that differentiation can be
monitored such that its onset can be identified when other phenotypic changes of differen-
tiation-specific marker-gene expression patterns are not yet apparent. Furthermore, by
calculating the slope/time ratios for each condition, the degree of induced differentiation
may also be obtained. As such, it is clear that ECIS represents a powerful technique for the
high-throughput screening of stem cells, which can be applied to nanomaterials and can be
performed noninvasively, in real-time, and label-free.
Microfluidic Flow Cytometry
Microfluidic flow cytometry (FC) is a technique that is also based on electrical impedance.
In the case of FC, single cells are continuously flowed between electrode pairs that are
energized using AC excitation signals at one or multiple frequencies [21] (Figure 19.3).
Owing to the fact that the area enclosed by electrode pairs approaches the diameter of
single cells, minute electrophysiological variations of individual cells can be detected and
then correlated to the impedance measurements obtained using this technique [22]. Unlike
ECIS, which is also based on impedance-based measurements, FC utilizes microfluidic
technology [23]. This renders the system highly compact by minimizing the size, weight,
and power requirements as well as the need for user intervention, resulting in a highly
autonomous system. In particular, microfluidics generally can be described as a set of
microchannels that are either etched or molded into a material (e.g., glass, silicon, or
polymer such as PDMS). These microchannels, which form the microfluidic chip, are
connected in a specific organization to achieve a desired function, which can include mix-
ing, pumping, cell sorting, or for chemical reactions. Finally, the microchannels are
(A)
Flow profile
AC current lines
Electrodes
A
B
C
(B)
t
tr
Cell
signal
Z
AC
-
Z
BC
0
0.5
1
1.5
2
t
/ms
Figure 19.3
Microfluidic impedance flow cytometer [23]. The cell passes over electrodes and the
impedance is measured. Information can be obtained about cell size, membrane, and cytoplasm
properties. Reproduced from Cheung
et al
., 2010 with permission from Wiley.
