(324b) Isomotive Dielectrophoresis (isoDEP): Characterization through Particle Velocemitry

Dielectrophoresis (DEP) is the translation of a polarizable particle when subjected to a non-uniform electric field. Most DEP devices focus on trapping or sorting particles and overlook its analytical capabilities. This work describes a parallel cell analytical system utilizing an isomotive dielectrophoresis (isoDEP) environment. With this approach detailed dielectric measurements of individual particles are possible.

The DEP force of a homogeneous spherical particle is F_DEP=2Ï?ε_ma³Re[f_CM](gradient(E²)) where ε_m is the permittivity of the fluid medium, a is the particle radius, f_CM is the Clausius-Mossotti factor, E is the electric field. The f_CM governs the magnitude and direction of DEP-induced motion and is a function of particle composition. The imaginary component of f_CM can be measured with electrorotation (ROT) [1,2] and the resultant rotational rate is a function of AC frequency as well as the dielectric properties of the media and cell. ROTâ??s most significant disadvantage is its limited throughput [1]. Further, a common characteristic of existing DEP electrode geometries is that the DEP force is significantly non-uniform in the sample region due to the gradient of the field-squared (gradient(E²)), making parallel analysis of cells non-trivial.

The unique characteristic of isoDEP is that the experimental region has a constant value of gradient(E²) resulting in a uniform DEP force inducing a constant (isomotive) particle translational velocity. Inspired by initial analysis by Herbert Pohl [3], we have developed a modified electrode geometry for isoDEP. Fabrication of extruded electrodes is straightforward via microfabrication methods (DRIE of conductive wafers) or sub-millimeter machining. A sample is injected and flow is halted before field activation. Digital images will extract particle size and, due a constant gradient(E²), the only unknown for each particle is f_CM. The field is applied and f_CM is extracted through particle tracking. The particleâ??s velocity will change as the AC frequency is swept over a specified range to obtain a comprehensive f_CM spectrum. Through simultaneous particle tracking such spectra are obtained for every particle in the imaging area, enabling parallel analysis of particles. In the future, isoDEP will be used to extract the dielectric properties of each cell (ex: membrane capacitance) â?? these properties directly correlate to the cell physiology.

References

[1] S.I. Han, Y.D. Joo, and K.H. Han, â??An electrorotation technique for measuring the dielectric properties of cells with simultaneous use of negative quadrupolar dielectrophoresis and electrorotationâ?, Analyst, 138, 1529, (2013).

[2] M. Cristofanilli,, G. De Gasperis, L. Zhang, M.-C. Hung, P.R.C. Gascoyne, and G.N. Hortobagyi, â??Automated electrorotation to reveal dielectric variations related to HER-2/neu overexpression in MCF-7 sublinesâ?, Clinical Cancer Research, 8, 615, (2002).

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