Substitution and spreadsheet methods for analysing dielectric spectra of biological systems

Abstract

1. Two major problems are encountered when one wishes to fit audio-and radio-frequency dielectric spectra of biological cell suspensions (or other materials): (a) changes in the apparent frequency-dependent permittivity of the system due to the phenomena of electrode polarisation can dominate those due to the biological system, and (b) because of the overlap of different dispersions it may be very difficult to deconvolute the individual contributions of the underlying biophysical mechanisms. 2. The extent of electrode polarisation depends substantially upon the conductivity of the medium surrounding the cells, but only marginally on the nature of the ions of a given valency contribution to it. 3. This, and the fact that the apparent time constants of the phenomena contributing to electrode polarisation are much greater than those of biological dielectric dispersions, permits one to use a simple substitution method to extract the latter in the presence of the former. This is shown both by simulation and by experiments using suspensions of human erythrocytes. 4. A spreadsheet method is described for the display of dielectric data and their conformance to the double Cole-Cole equation. The method provides a rapid and convenient approach, based on interactive graphical outputs, for the fitting of dielectric data to this equation. 5. Estimates derived from the spreadsheet program may be used in a BASIC program to arrive at the optimal fit. 6. The method is applied to the strongly-overlapping ~-and fl-dispersions of erythrocytes, permitting their deconvolution and providing a high level of accuracy.

Impedance-based tissue discrimination for needle guidance

“…Electrode polarization impedance (EPI) is a common problem in low frequency electrical bioimpedance measurements , Gabriel et al1996, Mirtaheri et al 2005Davey et al 1990. The EPI becomes more pronounced in highly conductive media , Gabriel et al 1996 or when using small electrodes .…”

“…If the calibration solution is chosen to approximate the EPI in the sample measurement, the properties of the investigated sample can be found by subtracting the EPI determined in the calibration measurement (Gabriel et al 1996 andDavey et al 1990). Since the EPI has been shown to be sample dependent , Gabriel et al 1996, Mirtaheri et al 2005and Bordi et al 2005, this method should only be used if the concentration of particles in the sample is low )(e.g.…”

On-Line, Real-Time Measurements of Cellular Biomass using Dielectric Spectroscopy

“…The polarisation control method (Schwan, 1963;Grant et al, 1978;Davey et al, 1990) is frequently used as an off-line method using the Biomass Monitor. A frequency scan of the cell suspension is performed and the conductance at the lowest frequency noted.…”

Modeling of Dielectric Permittivity of the Erythrocytes Membrane as a Three-Layer Model

“…Early studies of dielectric properties of the human erythrocytes are connecting with alternating current in the frequency domain were pioneered at the beginning of this century [12][13][14][15][16]. The frequency dependence of the dielectric properties of the RBC in suspension has been investigated by many scientists [17][18][19][20][21][22][23][24][25][26][27][28]. In the simplest model the RBC suspension is treated as an equivalent circuit for the measured capacitance and conductance [29].…”