ScienceAsia 33 (2007): 061-067 |doi: 10.2306/scienceasia1513-1874.2007.33.061
Optimizing the Electrode Shape for Four-electrode
Kanokkan Maswiwat2, Moritz Holtappels1 and Jan Gimsa 1*
ABSTRACT: Electrorotation experiments are conducted in harmonic rotating fields to characterize the passive
electric properties of cells or particles by their frequency-dependent rotation speed. The torque of the objects
is proportional to the square of the field strength. Therefore, a rotating field of constant amplitude is desirable
over a large area of the measuring chamber for reproducible measurements. In this study, the field distribution
in chip chambers was analyzed using numerical field simulation in combination with analytical post-processing.
The electric field distribution was compared for various electrode shapes. For the center, correction factors
could be calculated, relating the actual field strength to the quotient of electrode voltage and distance. Apart
from the center, the field was elliptically polarized with an eccentricity increasing with the distance from the
center. A spherical model object has been assumed to derive a theoretical expression for the torque induced
by an elliptical field. This model allowed us to consider the torque deviation for each site with respect to the
torque induced by the circular center-field. Various electrode shapes have been checked for minimum
deviations of the torque. We found the optimal chip design for electrorotation to feature electrodes with
KEYWORDS: rotating fields, four-electrode chambers, electrode design, torque, cell chip.
1 Institute of Biology, University of Rostock, Gertrudenstr. 11A, 18051 Rostock, Germany.
2 On leave from Department of Physics, Suratthani Rajabhat University, Amphur Muang, Suratthani 84100,
* Corresponding author, E-mail: email@example.com
Received 6 Mar 2006,
Accepted 26 Jul 2006