Dielectric measurement to monitor the growth and the physiological states of biological cells

Measurement of capacitance, also referred to as dielectric permittivity, is a new method of estimating the concentration of cells, monitoring the growth and detecting the physiological changes during the cultivation of organisms in various bioprocess. Several types of biological cells were studied, namely; Saccharomyces cerevisiae, Escherichia coli, Perilla frutescens (plant cells) and AFP-27 hybridoma cells. Generally, a linear correlation between cell capacitance (C) and other biomass measurement technique such as optical density (OD) and dry weight (DW) was obtained using the different types of cell suspension. Therefore, this method could be used to monitor the growth of the organism during the active growth. It could be conveniently used to make a rapid estimate of the cell concentration such as in plant cell suspension culture. The capacitance sensor could also be designed to be installed and autoclaved in-situ in a bioreactor and used for on-line monitoring of cell growth. On the other hand, distinct deviations in the capacitance value were observed in relation with the growth stage of the organism. This was observed in all the organisms studied but the type of deviation depends on the physiology of the organism. This variation in cell capacitance showed the possibility of using this method as a means to indicate changes in the physiological state of cells during cultivation. This capability would be very useful in designing control strategies that would depend on the physiological states in the bioprocess.Present address: Miles Inc., Berkeley, CA 94701 U.S.A.The authors sincerely appreciated the generosity of Dr. K. Mishima and Dr. A. Mimura of Kobe Steel Co., Japan. The useful discussions with M. Nakajima and technical assistance of J. Zhong and R. Pambayun were also acknowledged. The work in hybridoma cell culture was done through the collaboration with C. Perusich-Kussow and Prof. W. S. Hu, University of Minnesota, USA.