Automated electrorotation: dielectric characterization of living cells by real-time motion estimation

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Abstract
Electrorotation (ROT) has been applied widely for determining the dielectric properties of cells (and bio-particles) with single-cell resolution. However a serious limitation of ROT has been the tedious manual measurements required. A new real-time PC-based machine vision algorithm and hardware implementation are presented that achieve measurements of cell rotational motion and analysis of ROT spectra. The system is equipped with a computer-controlled quadrature digital synthesizer and is capable of measuring a ROT spectrum of a single cell with the frequency range 1 kHz-200 MHz in less than 5 min, taking four measurement points per frequency decade. Laser tweezers are used to facilitate cell selection and positioning in order to maximize the flexibility and accuracy of the system. The performance of this system is characterized in terms of robustness, accuracy and linearity with respect to manual measurements of real spinning cells under the influence of a rotating electric field. The system is quite generally applicable to a wide variety of mammalian cell morphologies and optical appearances. Membrane capacitance values derived from automated ROT measurements averaged within 10% of those obtained from manual measurements.