Dielectric spectroscopy of mammalian cells. 1. Evaluation of the biomass of HeLa- and CHO cells in suspension by low-frequency dielectric spectroscopy.

The capacitance of suspensions of CHO and HeLa cells (0.5-3 x 10(6) cells/ml) has been measured between 0.2 and 10 MHz. As frequencies decrease, there is a continuous increase in capacitance of both the cell suspension and the spent growth medium free of cells, a phenomenon which is partially attributed to an increased polarisation of the electrodes. At a given frequency, subtraction of the capacitance of the spent medium from that of the cell suspension allows one to determine the capacitance of the cells only. The intensity of this signal varies linearly with the biomass and cell size. At low frequencies such as those used in this study (0.25 MHz), where sensitivity is the highest, concentrations as low as 0.5 x 10(6) cells/ml can be accurately measured. Suggestions are made how to make these measures on-line, non-invasive and in real time.