(323b) Isomotive Dielectrophoresis Based Characterization of Chlamydomonas Cells

Isomotive dielectrophoresis
based characterization of Chlamydomonas cells

M.Z. Rashed¹, K.C. Grome¹, S.P.
Hendricks², S.J. Williams¹

1. University of Louisville, Louisville, Kentucky USA

2. Murray State University, Murray, Kentucky USA

Dielectrophoresis (DEP) is the phenomenon in which
a particle, such as a living cell, is moved by the interaction between a
non-uniform electric field and its induced polarization. Isomotive dielectrophoresis
(isoDEP) is a cell analysis and characterization
technique that uniquely utilizes a constant gradient field-squared (∇Erms2)
 resulting in a uniform DEP force. The resultant constant
(isomotive) particle
translational velocity that can be tracked using particle
tracking velocimetry (PIV) software
to extract the cell/particle
dielectric properties. The results obtained in this work are expected to
significantly enhance the research on characterization and differentiation of biological
cells.

The DEP force of a homogeneous
spherical particle is

FDEP =2πεma3RefCM∇Erms2 

fCM=εc*-εm*εc*+2εm*

where εc*, εm*
  are
the complex permittivity of the fluid medium and cell defined as ε^*=ε−
(σ/ω) j, a is the
particle radius, f_CM is
the Clausius-Mossotti factor, E is
the electric field.

In this work we have achieved
a cell characteristic analysis for Chlamydomonas cells (diameter:10-15 µm, Ph=8.5, suspended in a cultural medium (σ_m
= 19.3 mS/m) by using a  prototype isoDEP
device [1] that’s fabricated using deep reactive ion etching (DRIE) of a
conductive silicon wafer (1-10 Ω-cm) whose patterned features served as
electrodes and microchannel sidewalls simultaneously that are fabricated to
follow a specific curvature inherited from Pohl’s[2] electrode design to
ensure a constant (∇Erms2)
.

The AC frequency is swept over a specified range to obtain a
comprehensive f_CM spectrum of the Chlamydomonas
cells. If Re[f_CM] ,which is the real part of  f_CM function, which depends
on the angular frequency (ω) of the applied voltage. We noticed a negative
DEP (nDEP) force at frequencies below the estimated crossover frequency of 11.6
kHz, and a positive DEP (pDEP) starting from that frequency ,where cells
started to increase their translational velocities outward the high field with
increasing the frequency above the later frequency reaching the MHz range . It’s
noted that the cells’ viability can become uncertain after the application of
the AC signal (1000 V/m) for 10-12 mins [3] based on which requires
continuous inspection of the cells from time to time while conducting the
experiment – work is ongoing to assess the viability of exposed cells.

References

[1]   Allen, D.
J., Accolla, R. P. and Williams, S. J. (2017),
Isomotive dielectrophoresis for parallel analysis of individual particles. ELECTROPHORESIS.
doi:10.1002/elps.201600517.

[2]   H.A. Pohl, Dielectrophoresis: The Behavior of Neutral
Matter in Nonuniform Electric Fields, Cambridge; New York: Cambridge
University Press (1978).

[3]   Qian, Cheng
et al. “Dielectrophoresis for Bioparticle
Manipulation.” Ed. Bing Yan. International Journal of Molecular   Sciences 15.10 (2014): 18281–18309. PMC. Web.
16 Apr. 2017.