Biophysical Journal 63: 58-69 (1992)
© 1992 the Biophysical Society

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Dual-frequency dielectrophoretic levitation of Canola protoplasts

Karan V. I. S. Kaler ^*, Jing-Ping Xie ^*, Thomas B. Jones  and Reginald Paul 

Department of Electrical and Computer Engineering, University of Calgary, Calgary, Alberta, T2N 1N4 Canada
Department of Electrical Engineering, University of Rochester, Rochester, New York 14627 USA
Department of Chemistry, University of Calgary, Calgary, Alberta, T2N 1N4 Canada

ABSTRACT

A novel dual-frequency excitation technique is introduced which permits investigation of the low-frequency dispersion of Canola plant protoplasts using feedback-controlled dielectrophoretic levitation. The upper and intermediate frequency spectra obtained using the new technique are generally consistent with previous work. However, below some cross-over frequency f_OL, the protoplasts exhibit an apparent positive dielectrophoretic response that is not predicted by conventional theory. This cross-over frequency is linearly related to suspension conductivity, virtually independent of the suspension pH, and inversely proportional to the square of the cell radius. Examination of the complex Clausius-Mossotti polarization coefficient reveals that the observed positive dielectrophoretic response can not be accounted for in terms of Maxwell-Wagner polarization associated with a conventional layered model for the protoplast. The failure of straightforward enhancements to the protoplast model in explaining the low frequency behavior may indicate the presence of an electrophoretic contribution to the net observable force on the particle. To account for such fluid mechanical effects, it will be necessary to modify the existing dielectrophoretic force formulation.