Impedance spectroscopy of biological cells

Summary form only given as follows: A 6-electrode impedance chamber is used to perform wide bandwidth (1 Hz-3 MHz), high sensitivity, complex impedance measurements on living cells. Impedance measurements are performed under normal physiologic conditions to evaluate the electrical properties of living cells. The increase in sensitivity for the measurements, compared to cell suspension techniques, is accomplished by embedding the cells into the pores of a filter. This creates a “pseudo-epithelium” and markedly reduces the extracellular current pathways around the cells and consequently increases the sensitivity of the measurement. The advantages of this technique are discussed, as are the general insights and improvements in impedance measurements that are possible. In this technique, the cellular geometry and the portion of cell membrane under measurement are more precisely controlled than in suspension techniques. Essentially, the technique produces a multi-parallel, whole-cell, patch-clamp like structure. The resistance of the leak pathway is about 6-7×10⁷ Ω for each cell, compared to a gigaohm for the patch clamp resistance. The effects of: bandwidth mismatch between high-input impedance amplifiers, reference point drift due to solution resistivity changes, and the use of porous electrodes on the measured cellular impedance are discussed. The ability to alter extracellular solution temperature and composition, during an impedance experiment, provides a methodology to elucidate the underlying processes and structures responsible for the measured impedance. Lastly, the ability to electroporate the portion of the cell membrane under measurement, contributes another unique way to study the impedance of living cells