The tissue sample is broken up into single cells and held in a test tube, which is placed into the flow cytometer. The liquid containing the cells is drawn up from the test tube and pumped into the flow chamber.
Flow chamber – Cells flow through the flow chamber one at a time very quickly, about 10,000 cells in 20 seconds or 500 cells per second. This animation shows the cells moving in slow motion.
Laser – A small laser beam of very bright light hits the cells as they pass through the flow chamber. The way the light bounces off each cell gives information about the cell’s physical characteristics. Light bounced off at small angles is called forward scatter. Light bounced off in other directions is called side scatter.
Light detector - The light detector processes the light signals and sends the information to the computer. Forward scatter tells you the size of the cell. Side scatter tells you if the cell contains granules. Each type of cell in the immune system has a unique combination of forward and side scatter measurements, allowing you count the number of each type of cell.
Filters – The filters direct the light emitted by the fluorochromes to the color detectors.
Color detectors - As the cells pass through the laser, the fluorochromes attached to the cells absorb light and then emit a specific color of light depending on the type of fluorochrome. The fluorochromes on the cells act like the bar code on groceries as the cashier passes them over the scanner. In this case, there are two types of fluorescent markers: yellow and green. Any one cell can have one, both or none of the markers on its surface. The color detectors collect the different colors of light emitted by the fluorochromes. The fluorochrome data signal is also sent to the computer.
Computer – The data from the light detector and the color detectors is sent to a computer and plotted on a graph called a histogram.