In FACS (Fluorescence Activated Cell Sorting) cells can be measured for size and several fluorescence channels simultaneously and can be sorted for a chosen feature. The cells flow past a laser beam, which excites the fluorophores and a detector measures the fluorescence and the scattered light. During the meassurement, cells can be sorted (e.g. for high or low fluorescence or size exclusion). Since FACS can be performed with living cells, the sorted cells can be grown in culture after the sorting.