Small differences can be seen from their specifications, such as ramp rates, temperature accuracy and homogeneity, gradient range and even ergonomic features such as noise and easy operation.
However, what these specifications really mean can be difficult to say. Even less obvious are parts of the thermal cycler that cannot directly be seen. Some of these parts are critical for the performance of the thermal cycler and yet are not widely known to the users.
One of these elements is the PCR peltier. Peltiers are the component within a thermal cycler that are responsible for heating and cooling the metal block. The heat from the metal block will then be transferred into the chemical reaction within the plastic vessels. Almost all end-point PCR thermal cyclers in the market currently use peltier technology for heating and cooling.
However, there are differences in the peltiers used. One important criteria is quality. Quality PCR peltiers last longer and will give better temperature performance. Third party assessment such as one done by the Fraunhofer Institute, a leading material research facility in Germany, would provide a more objective reference than peltier manaufacturers’ specifications.
The second critical point of consideration is how the peltiers are assembled in the block. In simplified engineering, a functional thermal block is made up of the metal aluminum/silver block on top, the peltiers in the middle and the heat sink at the bottom. These three parts needed to be fixed together.
An important point to remember is that a PCR peltier is a sandwich of heating elements (Figure 1) and where you have a fixing point, there naturally cannot be any heating element. Hence, if the place where there is an absence of heating elements coincides with the location of the wells in the block above the peltier, there would be no direct heating of that particular well of the block.