On the audio- and radio-frequency dielectric behaviour of anchorage-independent, mouse L929-derived LS fibroblasts

Abstract

The utility of dielectric methods as a means for estimating the biomass of animal cells in suspension culture was assessed, using mouse L929-derived LS fibroblasts. The dielectric increment of the /3-dispersion was found to be a linear function of both cell number (30-70 permittivity units per lo6 cells/ml, depending on the batch of cells) and volume fraction in the range measured (up to 1.28 x 10s cells/ml. volume fraction = 0.14). The notional distribution of relaxation times as encompassed in the Cole/Cole a (0.13 kO.03 SD) was rather modest. If the cells were treated as spherical shell capacitors of their observable diameter and number, the apparent capacitance of the plasma membrane was some 1.9-4.0 pFF/cm2. This value significantly exceeded those (0.5-l pF/cm2) usually encountered or claimed, due predominantly to the possession by these cells of numerous plasma membrane protrusions. As the osmolarity of the suspending medium was increased using the non-permeant solute sorbitol, the apparent specific capacitance of the plasma membrane and the Cole/Cole a were increased, whilst the dielectric increment per 10" cells/ml was unchanged. In addition, a secondary /3-dispersion, with a characteristic frequency greater than that of the main P-dispersion, became increasingly prominent as the medium osmolatity was increased. It is proposed that this a,-dispersion is dominated by a Maxwell-Wagner mechanism taking place in the region of the plasma membrane protrusions of these cells.

On‐line biomass monitoring of CHO perfusion culture with scanning dielectric spectroscopy

“…Dielectric spectroscopy was first proposed for on-line biomass monitoring by Harris et al (1987), and has since found acceptance in many laboratory and industrial facilities worldwide. It has been used to monitor animal cell culture (Davey et al, 1988;Degouys et al, 1993;Ducommun et al, 2001a, Guan et al, 1998Noll and Biselli, 1998;Siano, 1997;Zeiser et al, 1999), plant cell culture (Markx et al, 1991) and microbial fermentation Gheorghiu and Asami, 1998;Krairak et al, 1999;Markx and Kell, 1995;Nicholson et al, 1996;November and van Impe, 2000;Penaloza et al, 1992;Siano, 1997).…”

On‐line determination of animal cell concentration in two industrial high‐density culture processes by dielectric spectroscopy

“…As described elsewhere (Davey et al, 1993), this technique induces an electrical ®eld in the culture and relates the variation of capacitance to biomass, which is then de®ned as the volume fraction of cells with intact plasma membranes, or biovolume . Successful applications of the Biomass Monitor Ò have been reported for various microbial (Fehrenbach et al, 1992;Harris et al, 1987;Salter et al, 1990) and insect cell (Zeiser et al, 1999) cultures, and for both free suspended and immobilized animal cell cultures Davey et al, 1988;Degouys et al, 1993). Dielectric spectroscopy has also been used in combination with heat¯ux measurement to assess speci®c rates in batch cultures of CHO cells (Guan and Kemp, 1999;Kemp and Guan, 1998).…”

Development of multi-frequency impedance scanning electron microscopy

“…Recently, the spatial resolution of infrared spectroscopies and Raman spectrum microscopes has been improved and those microscopes can be used simultaneously for observation and sample composition analyses at submicron resolution [ 9 , 11 , 12 ]. In contrast, the electrochemical impedance method measures the impedance of the whole sample and thus cannot provide structural information of the sample [ 13 , 14 ]. Several groups have reported imaging systems using electrical impedance tomography (EIT) at a few cm resolution [ 15 , 16 ].…”

“…Therefore, sample holders have been developed to enable observation of samples in liquids under atmospheric pressure [5][6][7][8]. In addition, the infrared spectrum microscope [9,10], Raman spectrum microscope and the electrochemical impedance spectroscope are generally used to analyse sample compositions [11][12][13][14]. Recently, the spatial resolution of infrared spectroscopies and Raman spectrum microscopes has been improved and those microscopes can be used simultaneously for observation and sample composition analyses at submicron resolution [9,11,12].…”