Particle Sensing: The Coulter Counter
Engineers Joseph and Wallace Coulter revolutionized many fields by developing an automated method to count red particles in solution; 50 years later, this scientist on a NASA ship in the Arctic uses a Coulter counter instrument to count the phytoplankton in water samples.Copyright Kathryn Hansen, NASA http://www.nasa.gov/topics/earth/features/icescape2010_plankton.html
Students are presented with a short lesson on the Coulter principle—an electronic method to detect microscopic particles and determine their concentration in fluid. Depending on the focus of study, students can investigate the industrial and medical applications of particle detection, the physics of fluid flow and electric current through the apparatus, or the chemistry of the electrolytes used in the apparatus.
The electrical sensing zone method of particle characterization, also known as the Coulter principle, was first proposed by electrical engineers Wallace and Joseph Coulter in the 1940s. This method was used to create a machine, the Coulter Counter Model A, that automated the counting of red blood cells and ushered in modern hematology. Today, many industries use similar machines to study particle number and size, including agriculture, biotechnology, environmental testing, food and beverage production, mining, paints and coatings, petrochemicals and pharmaceuticals.
After this lesson, students should be able to:
- Describe qualitatively how a particle changes the resistance between two electrodes as it moves through an aperture and how that resistance is measured.
- Describe the basic functioning of a Coulter counter, how the original Coulter counters improved blood cell counts, and how these improvements benefited patients and medical staff.