Fluorescent activated cell sorter (FACS)

Sometimes during the persuance of research in life sciences, we reach at a point where we need to detect and/or separate a particular type of cell when many types of cells are present in the sample for reasons beyond human control. For example, if we are transforming a bacterial cell with a plasmid/expression vector which is tagged with fluorescent protein such as green fluorescent protein or yellow fluorescent protein  of cells in our sample. We need to separate the transformed cells from the untransformed cells. Here this difficult work can be easily carried out by FACS equipment.  FACS has built in lasers that detect the fluorescence emitted by fluorescent molecules, thereby distinguishes between various types of cells and can separate them as well on this basis. The basic principle of FACS is to tag the desired cell with a fluorescent antibody or to express a fluorescent protein in the cell. The original reason of invention of FACS was for separating cells but with the passage of time this equipment started getting used for other subfunctions as well. Due to this FACS nowadays comes in two versions.

1 Basic equipment (Cell counter, detector)
2 Basic equipment with cell sorter

FACS can be used for the detection, quantification, characterization and/or sorting cells.

Proliferation Assays

Proliferation assays as the name suggests are used to the estimate the proliferation of  cells in the sample. Measuring cellular proliferation is important as in many pathological (diseased) and physiological (normal) conditions, proliferation varies depending on the situation. For instance, vascular smooth muscle cells, a type of cells found in the middle layer of blood vessels (arteries) proliferate as a part of disease of blood vessels (atherosclerosis). Proliferation assays measures metabolic rate of the cell more or less which is infact an index of the growing or dying or fixed situation of the cell. Metabolic rate is measured through activity of an enzyme converted in the form of a visible dye which is quantified by taking absorbance at a certain wavelength. These assays are very sensitive as they can detect very less change in cell. Some of the popular versions of proliferation assays are listed below.

MTT Assay
Alamar blue Assay