DOI 10.1140/epje/i2003-10143-2 Eur. Phys. J. E 14, 137–142 (2004) T HE EUROPEAN P HYSICAL JOURNAL E Ionic diffusion and space charge polarization in structural characterization of biological tissues M. Jastrzebska 1, a and A. Kocot 2 1 Medical University of Silesia, Department of Biophysics, Faculty of Pharmacy, 41-200 Sosnowiec, Ostrogorska 30, Poland 2 University of Silesia, Department of Biophysics and Molecular Physics, Institute of Physics, Universytecka 4, 40-007 Katowice, Poland Received 3 November 2003 / Published online: 22 June 2004 – c  EDP Sciences / Societ`a Italiana di Fisica / Springer-Verlag 2004 Abstract. In this study, a new approach to the analysis of the low-frequency (1–10 7 Hz) dielectric spectra of biological tissue, has been described. The experimental results are interpreted in terms of ionic diffusion and space charge polarization according to Sawada’s theory. The new presentation of dielectric spectra, i.e. (∂ε ′ /∂ ln f ) · f has been used. This method results in peaks which are narrower and better resolved than both the measured loss peaks and an alternative loss quantity ∂ε ′ /∂ ln f . The presented method and Sawada’s expression have been applied to the analysis of changes in the spatial molecular structure of a collagen fibril network in pericardium tissue exposed to glutaraldehyde (GA), with respect to the native tissue. The diffusion coefficient of ions was estimated on the basis of a dielectric dispersion measurement for an aqueous NaCl solution with a well-calibrated distance between the electrodes. The fitting procedure of a theoretical function to the experimental data allowed us to determine three diffusive relaxation regions with three structural distance parameters d s , describing the spatial arrangement of collagen fibrils in pericardium tissue. It has been found that a significant decrease in the structural distance d s from 87 nm to 45 nm may correspond to a reduction in the interfibrillar distance within GA cross-linked tissue. PACS. 77.22.-d Dielectric properties of solids and liquids – 87.14.-g Biomolecules: types 1 Introduction Dielectric spectroscopy is widely used to study the molec- ular dynamics and structure of different biological mate- rials including cell suspensions [1,2] and tissues [3–5]. The theoretical aspects and main findings in this subject have been reviewed [6–10]. It is commonly accepted that in the low-frequency region, dielectric dispersion in tissues is associated with ionic diffusion and interfacial polarization processes, although the extent of their contributions is difficult to establish, due to the complexity of both the structure and composition of the tissues. Classical Maxwell-Wagner or Bruggemann-Hanai mixture theories are less ap- plicable to the analysis of electrical response in most biological tissues. Raicu et al. [11] applied Bruggeman-Hanai theory com- bined with a dipole-dipole interaction to analyze the di- electric spectra of liver tissue at low frequencies. Recently, Dissado [12] proposed the use of fractal theory instead of the classical theory of interfacial polarization for the inter- pretation of low-frequency dielectric spectra of biological a e-mail: maja@slam.katowice.pl materials. Raicu et al. [13] interpreted a non-Debye di- electric behaviour of biological structures by their fractal nature. In spite of the remarkable potential of the fractal approach, this method does not provide a clear view of the dielectric properties of different tissue compartments. In this study, we present a new approach to the analy- sis of the low-frequency dielectric spectra measured for the porcine pericardium tissue. The experimental results are interpreted in terms of ionic diffusion and space charge po- larization according to Sawada’s theory. Sawada et al. [14– 17] gave the theoretical description of space charge polar- ization generated by the diffusive motion of ions and used this method to investigate the dynamics of mobile ions in liquid-crystal materials in the low-frequency region. In Sawada’s theory, the diffusive motion of ions under an AC field is restricted to the thickness of the specimen. As a result, both components of the dielectric permittivity are thickness dependent, which gives the possibility of ob- taining information about the dimensions of the different molecular compartments, e.g. in ions containing biological materials. We used a new presentation of dielectric spectra, i.e. a modified derivative loss quantity: (∂ε ′ /∂ ln f ) · f in order to achieve better separability of the relaxation regions. A