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. Laboratories are found in a variety of settings such as schools ...

apparatus most commonly used to amplify segments of

DNA Deoxyribonucleic acid (; DNA) is a polymer composed of two polynucleotide chains that coil around each other to form a double helix. The polymer carries genetic instructions for the development, functioning, growth and reproduction of al ...

via the

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

(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’ ...

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 init ...

. 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, with open reaction tubes. Later, the PCR process was adapted to the use of

thermostable DNA polymerase Thermostable DNA polymerases are DNA polymerases that originate from thermophiles, usually bacterial or archaeal species, and are therefore thermostable. They are used for the polymerase chain reaction and related methods for the amplification a ...

from ''

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

'', 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 physics, solid-state active heat pump which transfers ...

is commonly used. Quality thermal cyclers often contain

silver Silver is a chemical element; it has Symbol (chemistry), symbol Ag () and atomic number 47. A soft, whitish-gray, lustrous transition metal, it exhibits the highest electrical conductivity, thermal conductivity, and reflectivity of any metal. ...

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 a system that manipulates a small amount of fluids (10−9 to 10−18 liters) using small channels with sizes of ten to hundreds of micrometres. It is a multidisciplinary field that involves molecular analysis, molecular bi ...

chip. Thermal cyclers designed for

quantitative PCR A real-time polymerase chain reaction (real-time PCR, or qPCR when used quantitatively) is a laboratory technique of molecular biology based on the polymerase chain reaction (PCR). It monitors the amplification of a targeted DNA molecule duri ...

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

Modern innovation

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. 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