Thermoelectric Cooling Solutions

PCR Thermal Cyclers

The polymerase chain reaction (PCR) is a biochemical technology in molecular biology to amplify a single copy or a few copies of a piece of DNA across several orders of magnitude, generating thousands to millions of copies of a particular DNA sequence.

The method relies on thermal cycling, consisting of cycles of repeated heating and cooling of the reaction for DNA melting and enzymatic replication of the DNA. Primers (short DNA fragments) containing sequences complementary to the target region along with a DNA polymerase (after which the method is named) are key components to enable selective and repeated amplification. As PCR progresses, the DNA generated is itself used as a template for replication, setting in motion a chain reaction in which the DNA template is exponentially amplified. PCR can be extensively modified to perform a wide array of genetic manipulations.

Typically, PCR consists of a series of 20-40 repeated temperature changes, called cycles, with each cycle commonly consisting of the following main temperature steps. The cycling is often preceded by a single temperature step at a high temperature (>90°C), and followed by one hold at the end for final product extension or brief storage. The temperatures used and the length of time they are applied in each cycle depend on a variety of parameters.

  • Denaturation step: This step is the first regular cycling event and consists of heating the reaction to 94–98 °C for 20–30 seconds. It causes DNA melting of the DNA template by disrupting the hydrogen bonds between complementary bases, yielding single-stranded DNA molecules.
  • Annealing step: The reaction temperature is lowered to 50–65 °C for 20–40 seconds allowing annealing of the primers to the single-stranded DNA template.
  • Elongation step: The temperature at this step depends on the DNA polymerase used (commonly a temperature of 72 °C). At this step the DNA polymerase synthesizes a new DNA strand complementary to the DNA template strand. The elongation time depends both on the DNA polymerase used and on the length of the DNA fragment to be amplified.

PCR is carried out in special equipment called thermal cycler. The thermal cycler, also known as a thermocycler, PCR machine or DNA amplifier, is a laboratory apparatus most commonly used to amplify segments of DNA via the polymerase chain reaction (PCR). Thermal cyclers may also be used in laboratories to facilitate other temperature-sensitive reactions, including but not limited to restriction enzyme 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.

In modern PCR machines a thermoelectric modules are commonly used.

Here a unique advantage of thermoelectric module is used –cooling down and heating up very quickly and with fine temperature control. Moreover, thermoelectric modules for such applications have unique reliability which provide long operation of the cyclers.

There are cyclers where all probes (typically 48-96 units) cycled simultaneously by one program.

Recently PCR machines with individually cycling of each probe or small group of probes (1-4 units) have become more and more popular.

Usually a series of miniature thermoelectric modules is used for design of such machines. And every such module has an individual control electronic system.

The company RMT provides single-stage thermoelectric Peltier coolers (TECs) suitable for applications in PCR machines.

These are standard single-stage TECs, for instance of 1МС06 and 1МС10 series, but produced with use of special technique to increase reliability for long time cycling.

The company RMT regularly provides reliability testing of thermoelectric modules to keep particular reliability for such applications.

Please contact RMT concerning thermoelectric modules for applications in PCR machines, DNA amplifiers, particularly concerning selection of most optimal solutions.