A thermal cycler is a piece of laboratory equipment which is utilized to create the polymerase chain reaction process (PCR) which in turns amplifies DNA segments. Also known as a Thermocycler, a DNA engine thermal cycler, or a PCR Machine, the thermal cycler contains a thermal block with holes which hold tubes for containing the PCR samples. Temperature is then lowered or raised across the thermal block depending on the specifications of the test which is being run. The thermal cycler has programmable temperature increase/decease steps.
Early thermal cycler models were specifically designed with Klenow fragment DNA Polymerase I in mind. In this particular testing process, the enzyme would be rendered useless after each step in the heating amplification process. This made it mandatory to replace the enzyme with every step in the cycle. An automated pipettor with open tubes were used in this complicated early thermocycler.
The next models of thermal cycler were upgraded to utilize thermostable DNA polymerase from Thermus aquaticus. This upgrade allowed for a much more simplistic design of thermal cycler. A constant temperature oil bath was used to ensure a controlled temperature. Quality thermal blocks are constructed from silver to obtain the most uniformity of temperature throughout the block and the quickest temperature changes.
Today, the thermal cycler contains a thermoelectric heat pump, which allows for a solid state solution for temperature control without the need for a constant temperature bath. It is fitted with a heated lid which serves to press against the top of the sample tubes. This feature, in turn, hinders water condensation on the lid and removes the need to top off samples in the tubes with PCR oil. Higher end thermal cycler models have multiple thermal blocks which make multiple synchronous PCR reactions possible. The gradient thermal cycler allows the user to set different temperatures in specific sections of the thermal block, which is an extremely useful feature when testing appropriate temperatures for the annealing of primers.
DNA engine thermal cycler and PCR technology has increased greatly over the years with more advances to come.
