Abstract
Biological organisms and their component organs, tissues and cells have unique electrical impedance properties. Impedance properties often change with changes in structure, composition, and metabolism, and can be indicative of the onset and progression of disease states. Over the past 100 years, instruments and analytical methods have been developed to measure the impedance properties of biological specimens and to utilize these measurements in both clinical and basic science settings. This chapter will review the applications of impedance measurements in the biomedical sciences, from whole body analysis to impedance measurements of single cells and cell monolayers, and how cellular impedance measuring instruments can now be used in high throughput screening applications.
Highlights
Electrical impedance is defined as the opposition to an electrical current within a circuit
The electric dispersions in biological tissues in response to applied electric fields have been separated into three regions defined by frequency: alpha dispersion is seen at low frequencies (10 Hz–10 kHz) and is believed to be caused by the ionic environment immediately surrounding cells; beta dispersion occurs in midrange frequencies (10 kHz–10 MHz) and is due to capacitive charging of cell membranes; gamma dispersion occurs at higher frequencies (10 MHz–10 GHz) and is due to dielectric relaxation of water molecules [5, 6]
As impedance-based tumor detection depends upon the size of the tumor, the depth of the tumor from electrodes, and the relative difference in conductivity between the tumor and its surroundings, the primary applications of impedance in cancer detection have been in detecting cancers of the skin and breast, where tumors are localized within relatively small areas that are close to the skin and amenable to proximal electrode placement [19]
Summary
Electrical impedance is defined as the opposition to an electrical current within a circuit. More recently impedance measurements have been adapted to formats amenable to the analysis of individual cells or small cell populations, as add-ons to flow cytometry or Coulter counter instruments, and in multi-well formats to examine impedance characteristics of cell monolayers. These instruments are currently being utilized in high throughput screening approaches for drugs and bioactive agents in both academic and industrial settings, as well as for real time data collection in assays monitoring cellular activities such as death, activation, differentiation, migration and invasiveness. In this chapter we will review the various biological applications of impedance studies both in vivo and in vitro, and discuss the potential utility of in vitro studies as probes of the functional as well as molecular properties of pathologic cells and tissues
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