Final answer:
Cell surface granularity is measured with flow cytometry by detecting cell size and internal complexity using laser light scatter. Fluorogen-antibody conjugates label the cells, which are then separated into populations based on fluorescence using a fluorescence-activated cell sorter (FACS).
Step-by-step explanation:
Cell surface granularity is measured with flow cytometry using detectors that collect data from both forward- and side-scatter. These detectors measure the size and granularity of cells, respectively, as they pass through a laser beam. Specifically, side scatter is often associated with granularity or internal complexity of the cell, as it detects light scattered at a 90-degree angle from the laser-beam path.
Cells are labeled with fluorogen-antibody conjugates that are excited by the laser, and as they pass in single file through a capillary, they are individually counted and their relative fluorescence is recorded. The fluorescence intensity data are represented in a histogram with peaks corresponding to different populations of cells. The process can be taken a step further using a fluorescence-activated cell sorter (FACS), which is a form of flow cytometry that not only counts the cells but can also physically separate them into populations based on high and low fluorescence intensities.