page_title: Coulter counter
section_title: Development
hierarchical_section_title: Coulter counter / Development
caption_attribution_description: English: Coulter patented several different geometries that work with the Coulter Principle. (Image from US Patent #2,656,508)
context_page_description: A Coulter counter is an apparatus for counting and sizing particles suspended in electrolytes. It is used for cells, bacteria, prokaryotic cells and virus particles. The Coulter principle, and the Coulter counter that is based on it, is the commercial term for the technique known as resistive pulse sensing or electrical zone sensing.
  A typical Coulter counter has one or more microchannels that separate two chambers containing electrolyte solutions. As fluid-containing particles or cells are drawn through each microchannel, each particle causes a brief change to the electrical resistance of the liquid. The counter detects these changes in electrical resistance.
context_section_description: Wallace H. Coulter discovered the Coulter principle in the late 1940s, though a patent was not awarded until October 20, 1953. Coulter was influenced by the atomic bombs dropped on Hiroshima and Nagasaki. These events motivated Coulter to simplify and improve blood cell analysis so that large populations could be screened rapidly, as would be necessary in the event of a nuclear war. Partial funding of the project came from a grant award from the Office of Naval Research.
  Coulter was awarded US Patent #2,656,508, Means for Counting Particles Suspended in a Fluid. The Coulter principle is most commonly employed in a Coulter counter, which is an analytical instrument designed for a specific task such as counting cells. However, there are numerous other ways to implement the Coulter principle. Several of these have been attempted, some with commercial success, and some purely for academic research. To date, the most commercially successful application of the Coulter principle is in hematology, where it is used to obtain information about patients' blood cells.
  The Coulter principle relies on the fact that particles moving in an electric field cause measurable disturbances in that field. The magnitudes of these disturbances are proportional to the size of the particles in the field. Coulter identified several requirements necessary for practical application of this phenomenon. First, the particles should be suspended in a conducting liquid. Next, the electrical field should be physically constricted so that the movement of particles in the field causes detectable changes in the current. Finally, the particles should be dilute enough so that only one at a time passes through the physical constriction, preventing an artifact known as coincidence.
  While the Coulter principle can be implemented in a variety of designs, there are two that have become the most commercially relevant. These include an aperture format and a flow cell format. The figure above shows several other geometries that Coulter patented.
caption: Coulter patented several different implementations of the Coulter principle. Image taken from US Patent #2,656,508.
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