How Does a Coulter Counter Work?

A Coulter Counter is an instrument that can count and size the cells in an electrolyte to provide valuable information for researchers. For example, the number of cells of a certain type in a blood sample can provide clues to the type of disease that a patient is suffering.

High or low cell blood counts are significant in identifying diseases. A Coulter Counter is able to count the erythrocytes (red blood cells), leukocytes (white blood cells), and platelets. The instruments are commonly found in hospitals to help the medical staff determine the cell count of a patient’s blood sample – the ‘Complete Blood Count’. They are also useful for counting other types of cells such as bacteria, fat, muscle, and other types of cells.

With a Coulter Counter, an electrolyte containing the cells travels through a small aperture that is connected to an electric current. The count is achieved by observing the changes in voltage detected as either a cell or electrolyte travels through the aperture. For example, there may be a drop in current as a molecule passes through the aperture because the molecule is less conductive than the surrounding electrolyte. The voltage pulses provide insight into the volume of cells passing through in the suspension.

The first patent for the idea was filed in 1949 with the US Patent Office and issued in 1953 to American electrical engineer Wallace Coulter who was conducting research into the field with his brother Joseph Coulter. They were the individuals behind the Coulter Principle which defined how particles passing through a small hole at the same time as an electric current will have an impact on the reading based on their volume and the resulting measurable resistance in the electrolyte.

The system was set up to ensure that only one cell at a time could pass through the aperture. In an early test, they experimented by making a hole in cellophane covering a small capillary tube. They attached electrodes to the cellophane to create an electric current. In later versions, they focused on finding ways of automating the process.

After approval of their concept, they signed a contract for the Office of Naval Research in the USA to build the Coulter Counter instrument. They built their first version including a metering system, pulse counter, oscilloscope, and mercury manometer in 1952 and had this evaluated by the National Institutes of Health. Coulter Counters can use either direct current or alternating current depending on the type of research being carried out. Direct current versions are the most common but alternating current is useful for examining blood cells in hematology due to the properties of the cell membranes.

The brothers went on to refine the invention and set up Coulter Electronics in 1958. The system became commonplace for counting particles in electrolytes. The various patents outline the structure of the Coulter Counter and the adaptations over the years. The early version of the Coulter Counter was called Model A.

Their company grew as they developed new modifications. The later innovations incorporated developments in technology. For example, an early transistorized version was called the Model F.

The company Beckman eventually acquired Coulter Electronics in 1997 after it had already grown in size to thousands of employees.

Researchers from other organizations continue to make improvements to the Coulter Counter process. Some innovations have tried to increase the efficiency of systems. For example, Jun Hu and Jiang Zhe at the University of Akron have published a patent on a multichannel counting device.

Other companies are also involved in producing and refining their own versions of the Coulter Counters for sale such as Thermo Fisher. Beckman Coulter continues to innovate in the field with its own instruments. The technology has expanded its use from medical to other industries as well such as food manufacturing, ceramics, and molten metal.


Further Reading

Last Updated: Apr 4, 2023

Deborah Fields

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Deborah Fields

Deborah holds a B.Sc. degree in Chemistry from the University of Birmingham and a Postgraduate Diploma in Journalism qualification from Cardiff University. She enjoys writing about the latest innovations. Previously she has worked as an editor of scientific patent information, an education journalist and in communications for innovative healthcare, pharmaceutical and technology organisations. She also loves books and has run a book group for several years. Her enjoyment of fiction extends to writing her own stories for pleasure.


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  1. Isaac jacob Overseas Isaac jacob Overseas Nigeria says:

    Thank you for this amazing piece...

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