Counting cells with a Microchip based Coulter Counter

A particle counter using the Coulter principle has been developed. In a micro system the Coulter principle can be used for counting cells in a fluid flow but also for determining the size of each cell. In the original Coulter principle a coaxial flow of a sample containing cells and a sheathed electrolyte is passed through an orifice. When a cell passes the orifice it changes the resistance of the electrolyte from one side of the orifice to the other due to the volume displacement of the electrolyte. The Microchip Coulter counter is based on the original Coulter principle with a few changes added to the design, in order to obtain a wide range of sensitivity and long time stability. Many different Coulter counter designs have been fabricated with varying channel and orifice dimensions. Different kind of improvements have been suggested such as an adjustment of the sensitivity to the cell size and the integration of a four-point probe which could be used to improve the sensitivity of the recorded signal. The first Coulter counters have been tested with pure electrolyte to determine the electrical characteristics of the devices. Experiments with electrolyte containing calibration beads are under preparation and will be carried out during the next couple of months.