Microelectrodes electrical properties

From Eqs. (31) and (32) it can be calculated that 75% of the total resistance between a hemispherical microelectrode and a counter-electrode comes from a hemisphere with a radius of only 2dme and a semi-ellipsoid of a similar size can be defined for a circular microelectrode [49]. For that reason, the measured resistance reflects the electrical properties of a very small sample region. Microelectrodes can therefore serve as local conductivity probes on inhomogeneous solids as long as conductivity gradients occur on a much larger length scale than dme (Va/a dm J)> the conductivity in the 75% hemisphere is almost constant and the local conductivity obtained with circular microelectrodes reads... 

Electrodes can be divided into four categories according to their characteristic dimensions 1) Macroelectrodes, such as parallel plates, 2) Microelectrodes, 3) Ultramicroelectrodes, and 4) Nanoelectrodes. The four types of electrodes are illustrated in Figure 11 together with their characteristic electrical properties important for their applicability resistance, R, double-layer capacitance, Cdi, and current, /. 

CNT composite microelectrodes for recording and electrostimulation applications Fabrication, morphology, and electrical properties. Front Neuroeng., doi 10.3389/fneng.2012.00008. 

Gray, J. A. B. and Svaetichin, G., 1951, Electrical properties of platinum-tipped microelectrodes in Ringer s solution, Acta Physiol. Scand. 46 278-284. 

Schanne, O. F., Lavallee, M., Laprade, R., and Gagne, S., 1968, Electrical properties of glass microelectrodes, Proc. IEEE 56 1072-1082. 

Another important property of the outer membranes of nerve and muscle cells is their susceptibility to excitation under the effect of electric action. Excitation can be brought about, for example, by an external electric current pulse. Pulses can be applied to the membrane with the aid of two microelectrodes, one residing in the extracellular fluid and the other introduced through the membrane into the cytoplasm. 

Electrical bulk properties of ionic solids can be rather inhomogeneous (Sec. 3.1). In the following it is shown that microelectrodes are a very useful tool to gain spatially resolved information on the conductivity of such inhomogeneous solids. Let us first consider the case of a spherical microelectrode (radius rme) atop a sample with homogeneous bulk conductivity Ubuik- The bulk resistance R between the microelectrode and a hemispherical counter-electrode of radius rce (Fig. 12a) can be calculated by integrating the infinitesimal resistances of hemispherical shells according to... 

Laboratory-on-a-chip systems use immittance and dielectric variables measured with microelectrodes. In flow sensors, cell properties are measured with microelectrodes, and cell characterization and cell separation are performed. Properties of protein molecules have, for many years, been determined by the established methods of electrophoresis. Electrophoresis is based on the electric charge of cells and proteins, and the driving force exerted by an electric field. AU sorts of liquid suspensions with cells or bacteria can be measured with bioimmittance or permittivity. Cell adherence and cell micromotion can be monitored with microelectrodes equipped with a thin surface coating. 

---