Rotating biological cells in a non-rotating AC electric field

Electrically induced particle rotation (ROT) has been widely used to obtain particle effective conductivity and permittivity as a function of frequency and to distinguish particle types. Traditionally, a rotating AC electric field applied by microelectrodes rotates a single particle on an axis perpendicular to the electric field (Born-Lertes effect). However, producing a rotating electric field on microscale is often cumbersome, and does not permit the rotation (and analysis) of a large number of particles simultaneously.  Here we discuss and demonstrate rotation of cells in a non-rotating, non-uniform AC electric field using simple planar electrodes, with the axis of rotation perpendicular to the applied field. The rotation of the particle is asynchronous and is non-linearly dependent on the field strength and frequency. We present an electrohydrodynamic model for particle rotation and discuss our experimental observations of rotation. We also demonstrate the use of this technique for reconstruction of the 3D geometry of the cell, as a low cost alternative to stepping confocal microcopy, especially for a large number of single, non-adherent cells.