Flow cytometry uses light scattering caused by cells in a sample which are passed through a laser beam. This light scatters in the forward direction as well as the side direction and is called forward scatter, and side scatter respectively. Forward scatter is proportional to the size of the cell, while side scatter is proportional to the complexity of the cell. Both the forward and side scatter gets detected and converted into an electric pulse, which is directly proportional to the amount of scattered light. By combining these two signals into a graph, we get a so-called dot-plot which looks like this.
Let us examine such a dot-plot a bit closer:
On the x-axis we have the forward scatter, commonly abbreviated as FSC. On the y-axis we have the side scatter, commonly abbreviated as SSC. Each dot on this plot, represents one individual cell. By drawing a vertical line, anywhere along the x-axis, we know that all cells close to this line have a similar size. In the same way by drawing a horizontal line along the y-axis, all cells close to this line have a similar degree of complexity. In this manner by examining this graph a little bit more carefully, we quickly notice that several clusters of cells exist. By looking at the size and complexity of each cluster it is possible to determine what kind of cells are found there.
Now this is just the most basic flow cytometry graph available to us, and we can get even more information about the different cells by using a process known as flow cytometry FACS, which stands for “fluorescence-activated cell sorting.