Flow cytometry is also used as a detection method for sorting, identifying, and quantifying specific cells in complex matrices. A fluorescently tagged antibody is introduced/combined to a target antigen of choice (usually via a surface protein) and passed through a cytometer. The greater the amount of fluorescence emitted the larger the source (i.e. more of the target antigen). In addition, multiple fluorescently tagged antibodies of varied colors can be used to determine if multiple antigens are present in a matrix.