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.