During fluorescence-activated cell sorting (FACS), what is primarily measured?

In fluorescence-activated cell sorting (FACS), the primary measurement involves light scattering and light emission. This technique utilizes lasers to excite fluorescently labeled antibodies that bind to specific cell surface markers. When the laser light hits these labeled cells, they emit light at various wavelengths, which is detected and analyzed by the FACS equipment.

The light scattering helps to determine cell size and internal complexity, while the light emission provides information on the presence or absence of specific fluorescently tagged markers on the cells. This combination allows for precise sorting of cell populations based on specific characteristics, making this method highly valuable in research and clinical applications.

In this context, while size and complexity information is collected through light scattering, it is the measurement of light emission that is crucial for identifying and sorting the cells based on the fluorescent labels they carry, which directly relates to the fundamental purpose of FACS. Therefore, the focus on light scattering and light emission captures the essential function of this technology.