Bioimpedance Spectroscopy

In the context of biology, electrical phenomena are usually identified with ionic currents through protein channels, for example as they are postulated during nerve signalling (Andersen et al. Prog Neurobiol 88(2):104–113, 2009; Sakmann and Neher Annu Rev Physiol 46:455–472, 1984). However, there are more electrical phenomena that play a significant role in biological systems, namely those arising from polarization effects (Grimnes Bioimpedance and Bioelectricity, 2008; Polk Handbook of Biological Effects of Electromagnetic Fields 1996). Local inhomogeneities in charge distributions give rise to the formation of permanent molecular dipoles as in uncharged molecules such as (hydration) water, or due to the polar groups in proteins and lipid molecules. Non-permanent electrical dipoles can originate from the presence of ions in solution. Structured distributions of counter-ions at all polar interfaces, for example along the surface of proteins and especially along the polar membrane interfaces of cells, cause the formation of Stern and Helmholtz layers. All non-uniform distributions of charges and dipoles initiate and modify internal local electrical fields. Moreover, the application of external fields causes relaxation processes with characteristic contributions to the frequency-dependent complex dielectric constant. These dipolar relaxations were initially described by Debye (Polare Molekeln 1929). They are the basis of impedance spectroscopy (K’Owino and Sadik Electroanalysis 17(23):2101–2113, 2005; Schwan Adv-Bioland-Med-Phys (5):147–209, 1957; Schwan et al. J Phys Chem 66(12):2626–2635, 1962). The dispersion and the related adsorption contributions of the dielectric spectrum yield the dipole-specific relaxation frequencies and also give information about the dipole density. Redistributions of dipoles, binding events and changes in local viscosity will all appear as modifications of the signal amplitude and in systemspecific frequency shifts. These changes in the measured spectra can be used in a variety of technical devices, for example for biosensing as well as for monitoring the properties of cells in cell culture. B. Klösgen (B) Institute for Physics and Chemistry and MEMHYS – Center for Biomembrane Physics, University of Southern Denmark, Campusvej 55, 5340 Odense M, Denmark e-mail: [email protected] 241 B. Booß-Bavnbek et al. (eds.), BetaSys, Systems Biology 2, DOI 10.1007/978-1-4419-6956-9_11, C © Springer Science+Business Media, LLC 2011 242 B. Klösgen et al.