The thermal cycler (also known as a thermocycler, PCR machine or DNA amplifier) is a

laboratory A laboratory (; ; colloquially lab) is a facility that provides controlled conditions in which scientific or technological research, experiments, and measurement may be performed. Laboratory services are provided in a variety of settings: physic ...

apparatus most commonly used to amplify segments of DNA via the

polymerase chain reaction The polymerase chain reaction (PCR) is a method widely used to rapidly make millions to billions of copies (complete or partial) of a specific DNA sample, allowing scientists to take a very small sample of DNA and amplify it (or a part of it) ...

(PCR). Thermal cyclers may also be used in laboratories to facilitate other temperature-sensitive reactions, including

restriction enzyme A restriction enzyme, restriction endonuclease, REase, ENase or'' restrictase '' is an enzyme that cleaves DNA into fragments at or near specific recognition sites within molecules known as restriction sites. Restriction enzymes are one class o ...

digestion or rapid diagnostics. The device has a ''thermal block'' with holes where tubes holding the reaction mixtures can be inserted. The cycler then raises and lowers the temperature of the block in discrete, pre-programmed steps.

History

The earliest thermal cyclers were designed for use with the

Klenow fragment The Klenow fragment is a large protein fragment produced when DNA polymerase I from '' E. coli'' is enzymatically cleaved by the protease subtilisin. First reported in 1970, it retains the 5' → 3' polymerase activity and the 3’ → 5’ ex ...

DNA polymerase I DNA polymerase I (or Pol I) is an enzyme that participates in the process of prokaryotic DNA replication. Discovered by Arthur Kornberg in 1956, it was the first known DNA polymerase (and the first known of any kind of polymerase). It was initi ...

. Since this enzyme is destroyed during each heating step of the amplification process, new enzyme had to be added every cycle. This led to a cumbersome machine based on an automated

pipettor A pipette (sometimes spelled as pipett) is a laboratory tool commonly used in chemistry, biology and medicine to transport a measured volume of liquid, often as a media dispenser. Pipettes come in several designs for various purposes with diffe ...

, with open reaction tubes. Later, the PCR process was adapted to the use of thermostable DNA polymerase from ''

Thermus aquaticus ''Thermus aquaticus'' is a species of bacteria that can tolerate high temperatures, one of several thermophilic bacteria that belong to the ''Deinococcota'' phylum. It is the source of the heat-resistant enzyme ''Taq'' DNA polymerase, one of th ...

'', which greatly simplified the design of the thermal cycler. While in some old machines the block is submerged in an oil bath to control temperature, in modern PCR machines a

Peltier element Thermoelectric cooling uses the Peltier effect to create a heat flux at the junction of two different types of materials. A Peltier cooler, heater, or thermoelectric heat pump is a solid-state active heat pump which transfers heat from one side o ...

is commonly used. Quality thermal cyclers often contain

silver Silver is a chemical element with the symbol Ag (from the Latin ', derived from the Proto-Indo-European ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, white, lustrous transition metal, it exhibits the highest electrical ...

blocks to achieve fast temperature changes and uniform temperature throughout the block. Other cyclers have multiple blocks with high heat capacity, each of which is kept at a constant temperature, and the reaction tubes are moved between them by means of an automated process. Miniaturized thermal cyclers have been created in which the reaction mixture moves via channel through hot and cold zones on a

microfluidic Microfluidics refers to the behavior, precise control, and manipulation of fluids that are geometrically constrained to a small scale (typically sub-millimeter) at which surface forces dominate volumetric forces. It is a multidisciplinary field tha ...

chip. Thermal cyclers designed for

quantitative PCR A real-time polymerase chain reaction (real-time PCR, or qPCR) is a laboratory technique of molecular biology based on the polymerase chain reaction (PCR). It monitors the amplification of a targeted DNA molecule during the PCR (i.e., in real ...

have optical systems which enable fluorescence to be monitored during reaction cycling.

Modern innovations

Modern thermal cyclers are equipped with a heated lid that presses against the lids of the reaction tubes. This prevents condensation of water from the reaction mixtures on the insides of the lids. Traditionally, a layer of

mineral oil Mineral oil is any of various colorless, odorless, light mixtures of higher alkanes from a mineral source, particularly a distillate of petroleum, as distinct from usually edible vegetable oils. The name 'mineral oil' by itself is imprecise, ...

was used for this purpose. Some thermal cyclers are equipped with a fully adjustable heated lid to allow for nonstandard or diverse types of PCR plasticware. Cycler offen

Some thermal cyclers are equipped with multiple blocks allowing several different PCRs to be carried out simultaneously. Some models also have a ''gradient'' function to allow for different temperatures in different parts of the block. This is particularly useful when testing suitable annealing temperatures for PCR primers.

References

External links

OpenPCR
an open-source PCR thermal cycler {{DEFAULTSORT:Thermal Cycler Molecular biology laboratory equipment Polymerase chain reaction