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The dielectric properties of baby hamster kidney fibroblast (BHK(C-13)) cells have been measured using electrorotation before and after infection with herpes simplex virus type 1 (HSV-1). The dielectric properties and morphology of the cells were investigated as a function of time after infection. The mean specific capacitance of the uninfected cells was 2.0 microF/cm2, reducing to a value of 1. 5 microF/cm2 at 12 h after infection. This change was interpreted as arising from changes in the cell membrane morphology coupled with alterations in the composition of the cell membrane as infection progressed. The measured changes in the cell capacitance were correlated with alterations in cellular morphology determined from scanning electron microscope (SEM) images. Between 9 and 12 h after infection the internal permittivity of the cell exhibited a rapid change, reducing in value from 75epsilono to 58epsilono, which can be correlated with the generation of large numbers of Golgi-derived membrane vesicles and enveloped viral capsids. The data are discussed in relation to the known life cycle of HSV-1 and indicate that electrorotation can be used to observe dynamic changes in both the dielectric and morphological properties of virus-infected cells. Calculations of the dielectrophoretic spectrum of uninfected and infected cells have been performed, and the results show that cells in the two states could be separated using appropriate frequencies and electrode arrays.

It is a well-established fact that the torque exerted on polarisable particles in rotating electric fields varies across the volume between the field-generating electrodes. In this paper we quantify that variation by measuring the rotation rates of elliptical beads in 203 positions about an electrorotation electrode array. It is demonstrated that the torque varies in excess of 50% according to the position within the array. By processing the rotation data to determine the underlying trends, we find that the variation closely matches the predicted form of torque variation predicted by numerical models, and verifies the predictions of a previously proposed model of the action of variations the electric field on the induced rotation of particles.

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