(395c) Characterization of Streaming Dielectrophoresis Towards Rapid Particle Separation

Characterization
of streaming dielectrophoresis towards rapid particle separation

Monsur Islam, Rucha Natu and Rodrigo Martinez-Duarte

Mechanical Engineering Department, Clemson University, Clemson, SC, USA

Here we
present the initial results for the characterization of streaming dielectrophoresis
(DEP) towards rapid particle separation. DEP is termed as the motion of a
particle while exposed to a non-uniform electric field. In a traditional flow-through
DEP experiment, the DEP force (F_DEP)
dominates over the hydrodynamic drag force (F_DRAG)
and concentrates the targeted particles on the electrodes. In the case of streaming
DEP, the F_DRAG is
manipulated in such a way that the F_DRAG
overcomes the F_DEP and
carries away the DEP-concentrated particles from the electrodes. Hence,
concentrated and focused streams of particles are obtained at the end of the
electrode arrays (Figure 1a). Here we attempt to characterize and understand
how the quality of the streams (i.e. stream width, particle concentration, stream
position) depends on various experimental parameters such as electric field, flow
rate and electrode configuration. To date, we have performed experiments to
characterize the effect of applied voltage and frequency, and flow rate on the
stream width of 1 µm latex beads using a carbon
electrode DEP device. A potential application of streaming DEP may be rapid
cell concentration and separation for clinical diagnostics devices.

The
fabrication of the carbon electrode DEP device was detailed
elsewhere by our group [1]. For the DEP experiments, a particle suspension of 1
µm latex beads was prepared in distilled water to get a particle concentration
of 2.5 × 10⁷ particles/ml. The carbon electrodes were stimulated
with a sinusoidal signal. We varied the peak-to-peak magnitude of the signal between
7.5 V and 20 V. The frequency was varied between 5 kHz
to 2.5 MHz to target positive DEP of the particles. Flow rates ranging from 25
µl/min to 300 µl/min were used for the experiments. We
captured the image of the flow of the particles at the end of the electrode
arrays 1 minute after turning on the electric field. The images were analysed
to find the stream width using the image-processing software ImageJ. At least
three experiments were performed for each combination of the experimental
parameters.

Results of
the experiments are shown in Figure 1. Three regions are defined in the
figures: Trap, Stream and Escape. The “Trap” region indicates the phenomenon
when all the particles were trapped on the electrodes and no streams were
observed at the end of the electrodes due to much stronger F_DEP over the F_DRAG.
“Stream” represents the conditions when focused streams of particles could be
observed at the end of the electrodes due to weak dominance of the F_DRAG over the F_DEP. “Escape” indicates the
incidence when no focusing was observed due to the
strong dominance of F_DRAG over
the F_DEP. In Figure 1b, 1c
and 1d, it should be noted that in each case the stream gets wider while moving
from “Trap” region to “Escape” region. The F_DRAG
becomes stronger over the F_DEP
as we move from “Trap” region to “Escape” region. The stronger F_DRAG restricts the focusing
of the particles by the F_DEP,
which makes the streams wider.

The ongoing
work is to build a computational model with respect to F_DEP and F_DRAG.
The objective of this model is to predict the occurrence of the stream and its
quality by plugging in any of the experimental parameters to the model. A
COMSOL simulation is also being used to investigate the effect of different
electrode configurations on the streaming DEP. The future work includes design
and fabrication of certain chambers downstream of the microchannel to retrieve
the focused particles for further processes.

References:

ADDIN Mendeley
Bibliography CSL_BIBLIOGRAPHY [1]      R.
Martinez-Duarte, P. Renaud, and M. J. Madou, “A novel approach to
dielectrophoresis using carbon electrodes.,” Electrophoresis, vol. 32,
no. 17, pp. 2385–92, Sep. 2011.

Figure 1: (a) Focusing of 1µm latex beads using positive DEP; Results
showing how the stream widths of 1 µm latex beads changes with respect to (b)
flow rate, (c) frequency of the applied field, and (d) peak-to-peak voltage.