Cytometer means any device, which can count the number of cells. Flow cytometry is an amazing instrument which can count the number of cells in flowing state. It is a laser-based technology, which not only counts a given type of cell but also analyse the analytes characteristics and sort the different types of cells in the sample.

The flow cytometry has four different components

Fig 1: Working of a flow cytometer

The fluidics: As mentioned earlier the cells are counted in the flowing state. The cells are flowing, and the fluidics causes the cells to flow in a single file using the sheath fluid which flows around the sample. The velocity of the sheath fluid is adjusted such that it drags the sample components and forces them to flow in a stream with diameter allowing single cell through. This is known as Hydrodynamic focussing

Laser/s: Is the source of light of single wavelength. The laser beam hits the cells which are flowing in the single file, which causes scattering of the laser light. The light is scattered in the forward direction as well in the other directions by the cell.

Optics and detectors: The light is detected by a detector placed in the forward plane, which collects the forward scatter. Another detector is placed at perpendicular to the forward plane which detects the side scatter. The dichroic filters are placed in the path of the side scatter which allows the light of particular wavelength to be detected by the detector.

Electronics: When a cell passes through the path of laser beam and scatters the light, it is recognized by the detector. In the detector it is recognized as signal, as a electric current. The magnitude of the current is proportional to the number of photons scattered by the cell.

The forward scatter is actually the representative of the cells size and side scatter of the cells granularity. The forward scatter and the side scatter is plotted on the graph, which gives count of cells of each types.

Cells can be differentiated with help of the fluorescently labelled antibodies specific for the cell type and help in the count and sorting of the cells.

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