Hydrodynamic focusing is a technique used to provide more accurate results when using

flow cytometer Flow cytometry (FC) is a technique used to detect and measure physical and chemical characteristics of a population of Cell (biology), cells or particles. In this process, a sample containing cells or particles is suspended in a fluid and inject ...

s or

Coulter counter A Coulter counter is an apparatus for counting and sizing particles suspended in electrolytes. The Coulter counter is the commercial term for the technique known as resistive pulse sensing or electrical zone sensing, the apparatus is based on T ...

s for determining the size of

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...

cells Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Locations * Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery w ...

Technique

Measuring particles

Cells are counted as they are forced to pass through a small channel (often referred to as a flow cell), causing disruptions in a

laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The fir ...

light beam or electricity flow. These disruptions are analyzed by the instruments. It is difficult to create tunnels narrow enough for this purpose using ordinary manufacturing processes, as the diameter must be in the magnitude of micrometers, and the length of the tunnel should exceed several millimeters. The standard channel size used in most production flow cytometers is 250 by 250 micrometers.

Focusing with a fluid

Hydrodynamic focusing solves this problem by building up the walls of the tunnel from fluid, using the effects of

fluid dynamics In physics and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids— liquids and gases. It has several subdisciplines, including ''aerodynamics'' (the study of air and other gases in motion) an ...

. A wide (hundreds of micrometers in diameter) tube made of glass or plastic is used, through which a "wall" of fluid called the sheath flow is pumped. The sample is injected into the middle of the sheath flow. If the two fluids differ enough in their velocity or density, they do not mix: they form a two-layer stable flow.

Sources

References

Microbiology techniques {{Microbiology-stub