Biomedical Engineering Reference
In-Depth Information
5.3.4 Dielectrophoretic Traps
In 1995, Peter Gascoyne's group from the University of Texas Anderson Cancer Center (Houston,
Texas) built the irst device capable of trapping
and
sorting suspended cells, and to achieve the
feat, they used dielectrophoresis (DEP, see Section 3.3.3). hey constructed a 60-μm-deep glass
plate chamber with interleaved gold electrodes at its bottom surface and introduced a diluted
blood suspension containing tumor cells (normal/cancerous cell ratio = 3:1) into the chamber
in the direction orthogonal to the electrodes. Upon applying a 200 kHz 5V peak-to-peak sinu-
soidal signal to the electrode array for 30 seconds, the tumor cells were observed to concentrate
by positive DEP on the electrode tips (
Figure 5.20a
), whereas all the blood cells were removed
with the eluate (
Figure 5.20b
).
In 1997, Tomokazu Matsue and coworkers irst applied DEP to micropattern cells. An
array of microelectrodes was placed approximately 50 μm away from the cell culture surface,
with cellophane tape acting as the spacer. When a dense cell suspension (~10
6
cells/mL) was
allowed into the gap, voltages (~7 V
rms
) applied to the microelectrodes repelled or attracted
the cells depending on the applied frequency. Water electrolysis was avoided by applying
high frequency (>3 kHz) ields. Micropatterning of mouse myeloma (nonadhesive) cells was
demonstrated. he frequency dependence of the sign and magnitude of the dielectrophoretic
force was also used by van den Berg and Lammerink to selectively position cells on sub-
strates. he ield, applied perpendicularly to the cell surface, repels cells at frequencies on
the order of 10
6
Hz and higher and attracts them at lower frequencies. At high electric ield
magnitudes of approximately 50 kV/m, local heating of a few degrees centigrade was observed.
Because ibroblasts only grow and attach between 30°C and 40°C, selective attachment in
cold (30°C) medium and selective detachment in hot (40°C) medium occurred on the locally
heated areas.
A collaborative team from the Center of Engineering in Medicine (Massachusetts General
Hospital) and MIT led by Martin Schmidt has presented arrays of DEP traps that allow for
selectively trapping and sorting single cells in suspension (
Figure 5.21
). he cylindrical shape of
the electrodes increases the trapping eiciency of the electrodes compared with a normal planar
tetrode. In this design, the DEP force is used to counteract the drag forces from the luid, which
is continuously lowing; as soon as a given trap is turned of, the cell is taken away by the low
(see
Figure 5.21d
and
e
) and can be collected in a separate channel.
DEP forces have been used not only to trap cells in aqueous media but also cells encapsulated
in gel microspheres, within a gelling medium, to create “3-D tissue constructs” (see
Figure 7.4
in Section 7.1.1).
DEP electrode
a
b
Outlet area
MDA231 human metastatic breast cancer cells
Blood cells
Flow
Flow
80 µm
FIGURE 5.20
Dielectrophoretic.trapping.of.cells..(From.Frederick.F..Becker,.Xiao-Bo.Wang,.Ying.
Huang,.Ronald.Pethig,.Jody.Vykoukal,.and.Peter.R..C..Gascoyne,.“Separation.of.human.breast.can-
cer.cells.from.blood.by.differential.dielectric.afinity,”.
Proc. Natl. Acad. Sci. U. S. A.
.92,.860-864,.
1995..Copyright.(1995).National.Academy.of.Sciences,.U..S..A.)
