Micromotion of mammalian cells measured electrically

Motility is a fundamental property of mammalian cells that normally is observed in tissue culture by time lapse microscopy where resolution is limited by the wavelength of light. This paper examines a powerful electrical technique by which cell motion is quantitatively measured at the nanometer level. In this method, the cells are cultured on small evaporated gold electrodes carrying weak ac currents. A large change in the measured electrical impedance of the electrodes is observed when cells attach and spread on these electrodes. When the impedance is tracked as a function of time, fluctuations are observed that are a direct measure of cell motion. Surprisingly, these fluctuations continue even when the cell layer becomes confluent. By comparing the measured impedance with a theoretical model, it is clear that under these circumstances the average motions of the cell layer of 1 nm can be inferred from the measurements. We refer to this aspect of cell motility as micromotion.