The Coulter counter is named for its counting principle; which principle does it use?

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Multiple Choice

The Coulter counter is named for its counting principle; which principle does it use?

The essential idea is that counting and sizing come from measuring changes in electrical impedance as particles pass through a small opening in a conductive fluid. When a cell or particle traverses the aperture, it displaces electrolyte and momentarily changes the resistance between two electrodes, producing a short voltage pulse. The pulse’s height is proportional to the particle’s volume, so each pulse counts one particle and its amplitude estimates its size. This is the Coulter principle—using electrical impedance to detect and size microscopic particles. Magnetic susceptibility, acoustic impedance, and optical scattering describe other sensing methods that rely on magnetic properties, sound waves, or light, respectively, not the electrical impedance changes that define the Coulter counter.

The essential idea is that counting and sizing come from measuring changes in electrical impedance as particles pass through a small opening in a conductive fluid. When a cell or particle traverses the aperture, it displaces electrolyte and momentarily changes the resistance between two electrodes, producing a short voltage pulse. The pulse’s height is proportional to the particle’s volume, so each pulse counts one particle and its amplitude estimates its size. This is the Coulter principle—using electrical impedance to detect and size microscopic particles.

Magnetic susceptibility, acoustic impedance, and optical scattering describe other sensing methods that rely on magnetic properties, sound waves, or light, respectively, not the electrical impedance changes that define the Coulter counter.

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