Considerations for purchasing

There are several factors to bear in mind when considering the purchase of a thermal cycler.

1) Temperature change

Most thermal cyclers use a Peltier element to regulate the control of the temperature block. Ideally, the thermal cycler would change the temperature inside the reaction tubes instantaneously. In practice, it changes the temperature immediately surrounding the outside of the sample tube. For the reactions to work properly, the temperature needs to be changed at precise times and as quickly as possible. Ideal conditions would include having the fastest possible temperature change, but some types of work may not require the fastest of the fast—how fast depends on your particular experimental needs.

All thermal cycler manufacturers aim to make heating blocks that change temperature uniformly and as quickly as possible. If fast temperature changes are important to your work, look for thermal cyclers with a heating block made of silver. Silver heating blocks work best for fast temperature changes, and for encouraging temperature uniformity throughout the heating block, because silver conducts heat better than other materials used for heating blocks.

2) Capacity and vessel type

The thermal cycler block comes in a variety of sample capacities, with wells for sample tubes numbering up to 384, for example.

The issue of capacity is also related to the type of containers that you plan to use for the individual PCR reactions. The ubiquitous 0.2-mL PCR tube is still the most commonly used PCR reaction vessel. However, it is also possible to find thermal cycler blocks that can hold a variety of other containers, including 0.5-mL PCR tubes, yet more tubes that are distinct from the traditional PCR tubes (such as larger conical tubes), multiwell plates, and tube strips.

3) Heated lid

In times past, researchers added a layer of mineral oil to the top of each PCR reaction to prevent the reaction fluid from evaporating and condensing on the inside of the tube lids. Today, instead of dealing with messy mineral oil, many thermal cyclers are equipped with a heated lid that lies on top of the samples in the temperature block, preventing evaporation and the resulting condensation. This is not just a matter of convenience—evaporation and condensation can lead to data disaster, even more so in small-volume samples, because they change the concentration of reagents in the PCR tubes, which of course can result in skewed results or unwanted variation. A specialized, heated thermal cycler lid can help to prevent these problems, especially for sample tubes at the edges and corners of the heating block, which are more vulnerable to evaporation and condensation.

4) Flexibility, modularity, and adaptability

In earlier thermal cycler models, and indeed in some of today’s high-quality models, the heating block was one solid component. Today many manufacturers offer thermal cyclers with interchangeable heating blocks. This is useful if you need to use a different number of samples, or a different kind of reaction vessel, for example, changing from PCR tubes to multiple-well plates.