Dielectric Breakdown of Cell Membranes

Abstract

A Coulter Counter is a measuring device for counting and sizing non-conducting particles suspended in a conducting medium. This instrument is based on the principle that the electrical resistance in a small orifice, across which a voltage is applied, will change when a suspension of non-conducting particles is sucked through it. The current or voltage pulses arising are, to a first approximation, proportional to the size of the particles (size = shape factor X volume); this means that after linear electronic amplification and subsequent pulse height analysis the size distribution of each population under investigation can be obtained. Using conventional Coulter Counters, however, the measured size distribution is generally strongly distorted (skewed) due to inhomogeneities in the electric field strength in and near of the orifice; the pulse height becomes dependent on the path and orientation of each particle in the orifice (GROVER et al., 1969a, b, 1972; THOM, 1972). As described previously (ZIMMERMANN et al., 1973) the distortion arising from the inhomogeneous field can be eliminated by hydrodynamic focusing of the suspension flow. Then the particles travel on the same pathway, parallelly oriented, along the central axis through the orifice, and a true measurement of the real size distribution of the population can be obtained.