(185c) Rapid Cell Separation Using 3D Carbon Electrode Dielectrophoresis

Rapid
cell separation using 3D carbon electrode dielectrophoresis

Monsur Islam, Rucha Natu and Rodrigo
Martinez-Duarte

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

Here
we present the initial results for rapid separation of two different particles
from a particle mixture using carbon electrode dielectrophoresis (DEP). Isolation
and concentration of pathogenic cells are one of the important steps in
clinical diagnostic systems. Expensive and large laboratory equipment such as
fluorescence activated cell sorting (FACS) are generally used for cell
isolation; in a process that is relatively expensive and can take several
hours. Here we propose a DEP-based microfluidic platform for rapid separation and
concentration of cells. Preliminary results indicate separation of Candida
albicans and latex beads of 10 µm diameter from the cell-particle mixture
at a flow rate of 100 µl/min using streamingDEP.

C.
albicans cells
were grown in yeast malt broth (YMB, Sigma Aldrich, USA) culture for 2 days in
a controlled environment at 37 °C. 150 µl of this cell culture was then
inoculated in 4 ml of experimental buffer solution which contained 15% sucrose,
0.5% dextrose and 0.1% bovine serum albumin (BSA). The experimental cell
suspension was prepared by washing and re-suspending the cells in the buffer
solution. The concentration of the cell suspension was 7.18 x 10⁶
cells/ml. A particle suspension of 10 µm latex beads was also prepared in the
buffer solution and concentration was measured 5.86 x 10⁶
particles/ml. A mixture solution was also prepared by mixing the cell
suspension to the particle suspension in a 1:1 volume ratio.

The
fabrication of the carbon electrode DEP device was reported elsewhere by our
group [1]. DEP experiments were performed for both cell
suspension, particle suspension and mixture solution. The carbon electrodes
were stimulated with sinusoidal signal having magnitude of 20 Vpp and frequency
of 250 kHz. At this conditions, C. albicans experience positive DEP and
the 10 µm latex beads experience negative DEP. A constant flow rate of 100
µl/min was maintained throughout the experiments. At the cell density used in
this work this would represent a throughput of ~10⁵ cells/min. The
continuous separation principle shown here is based on attracting the targeted
cell towards the electrode but not trapping it. Hence, an equilibrium between
the positiveDEP and hydrodynamic drag force is sought. Streaming behaviour of C.
albicans is illustrated in Figure 1a. Instead of streaming, latex beads experience
focusing by negativeDEP and were focused in between the electrodes (Fig. 1b).
When using the mixture solution, both the above mentioned phenomena occurred
simultaneously and C. albicans and latex beads focused and flowed along
different streamlines showing separation in Fig 1c. The results obtained when
the electric field is off are shown in Fig. 1d, showing how the lines
disappeared.

Ongoing
work is to determine the maximum flow rate while still observing streaming
behaviour. To this end, COMSOL is being used to determine the position of the
streamlines at different flow rates. The fabrication of geometries that would
allow for the continuous retrieval of the focused cells represents future
efforts in this work.

References:

[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: Focusing of (a)
C. albicans using positive DEP, (b) 10 µm latex beads using negative
DEP; (c) Separation of C. albicans from 10 µm latex beads; (d) No focusing
is observed when the field is turned off. The DEP parameters were 20 Vpp
magnitude and 250 kHz frequency and the flow rate was 100 µl/min. Images taken
at a rate of 100 fps.