Dielectrophoretic Orientation, Manipulation and Separation of Live and Heat-Treated Cells of Listeria on Microfabricated
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Dielectrophoretic Orientation, Manipulation and Separation of Live and Heat-Treated Cells of Listeria on Microfabricated Devices with Interdigitated Electrodes 1 Haibo Li , Rashid Bashir1,2,* 1 School of Electrical and Computer Engineering, 2Department of Biomedical Engineering Purdue University, West Lafayette, IN 47907-1285 Abstract Dielectrophoresis, the movement of particles in non-uniform AC electric field, was used to separate live and heat-treated Listeria innocua cells with great efficiency on micro-fabricated devices with interdigitated electrodes by utilizing the difference of dielectric properties between live and dead cells. Both live and dead cells are found to be only able to collect either at the centers of the electrodes in negative dielectrophoresis or at the electrode edges in positive dielectrophoresis. Cell viability was characterized by a rapid method using epifluorescence staining. The dependency of the applied AC signal’s frequency on the dielectrophoresis of different cells, as well as the orientation of the cells on the electrodes in the dielectrophoresis, is also observed and discussed. This on-electrode manipulation and separation of cells can prove to be useful in micro-scale diagnostic applications in biochips. Introduction Dielectrophoretic forces [1] occur on cells when a non-uniform AC electrical field interacts with field-induced electrical polarization. The time-averaged dielectrophoretic force F for a dielectric sphere immersed in a medium in constant field phases in space (like the situation in our experiments) is represented as F = 2πε 0ε m r 3 Re[ f CM ]∇ E RMS
2
(1)
where ε 0 is the vacuum dielectric constant, r is the particle radius, ERMS is the root mean square value of the electric field, and f CM is well-known as the Clausius-Mossotti factor: f CM
ε *p − ε m* = * ε p + 2ε m*
(2)
where ε *p and ε m* are the relative complex permittivities of the particle and the medium respectively. When the dielectric constant of particle is larger than that of medium, i.e., Re[ f CM ] > 0 , the DEP is called positive and the particle moves towards the locations with the greatest electric field gradient. Whereas, when the dielectric constant of particle is smaller than that of medium, i.e., Re[ f CM ] < 0 , the DEP is called negative and particle moves to the locations with smallest electric field gradient. Dielectrophoresis has been employed successfully in isolation and detection of sparse cancer cells, concentration of cells from dilute suspensions, separation of cells according to specific dielectric properties, and trapping and positioning of individual cells for characterization [2], for example, for separations of viable and nonviable yeast cells [3-4], several species of bacteria [5*
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