Reduction of the contribution of electrode polarization effects in the radiowave dielectric measurements of highly conductive biological cell suspensions

Electrode polarization effects in dielectric spectra of highly conductive b iological cell suspensions cause a severe difficulty in the estimation of d ielectric parameters of cells under physiological conditions. This problem becomes particularly serious with the increase of the electrical conductivi ty of the sample, preventing the use of low frequencies in the characteriza tion of biological systems, especially aqueous biological systems. Although a variety of methods to correct the electrode polarization have be en proposed in the past, no simple technique for its correction has been av ailable so far, Since the magnitude of the polarization effect can be time- dependent owing to changes in the conductance of the suspending medium or t o possible alteration in the electrode surface structure, it is clear that correction procedure should be based on a kind of "self-correction" method, avoiding the so-called "comparison methods" which, on the contrary, requir e time-independent effects. This note is aimed to address this problem considering an electrode polariz ation modelled by a constant phase angle (CPA) element in series with the s ample admittance. A scaling-law frequency dependence has found to describe the a.c. response of the interface between the electrode and the bulk elect rolyte solution. Although this approach has been extensively proposed in th e past in the analysis of dielectric spectra of biological suspensions, we have somewhat modified the way it has been previously applied and have re-e xamined in detail its effectiveness in typical systems of biological intere st. The results give support to the proposed analysis, allowing the complet e low-frequency dielectric spectra characterization at frequencies of the o rder of 1 kHz for samples with a bulk ionic conductivity as large as that o f the order of 1 mho/m. Typical examples with different dielectric behaviou rs are extensively discussed in order to show the applicability of the prop osed method to biological samples. (C) 2001 Elsevier Science B.V. All right s reserved.