Apart from the material/ coating of the block, the related heating and cooling source is crucial for a high-quality PCR cycler. The temperature is adjusted by Peltier elements, a process also known as thermoelectric cooler.
The Peltier element is based on the Peltier function (developed by Jean Peltier). The flow of power inside the element ends up in a change of temperature. Depending on the direction of the power flow, the element can heat or cool.
The elements are smaller, lighter and less fragile compared to a compressor-based cooling. In contrast to heating foils, you can also use them for cooling. The drawback of the Peltier element is the high power needed for a relatively low temperature change. By using a fan, you can remove the heat from the element and improve the efficiency of the system.
Using a fan to remove the heat from the element improves system performance. That is why most PCR cyclers have one or more fans. To reduce the risk of contamination at the bench, the fan exhaust air should be directed to the back of the instrument.
For an optimal and safe usage of the PCR block, the Peltier elements should cover the complete block.
Block format types
For optimal PCR results, the reaction conditions should be optimized: thin-walled vessels and a reaction volume which can be temperature-treated in a good way. That means, the temperature transfer from the block towards the tube (and respectively the sample) should be homogenous. The more volume of the sample is surrounded by the metal well walls of the block, the better the temperature transfer. Years ago, most PCRs were performed in 0.5 mL vessels. Due to optimization, today, most people focus on 0.2 mL vessels, 0.1 mL strips, or 96-well PCR plates. Still, there are some applications where 0.5 mL vessels are useful.
There are 4 different blocks known as standard blocks:
- Universal block:
Combined pattern for 0.1, 0.2 and 0.5 mL vessels 0.2 mL vessel/ 96-well
- PCR plate block:
Standard block for up to 96 vessels
- 384-well block:
Optimal for high throughput applications in 384-well plates.
- In-situ block:
Space for up to 4 slides to be used for in-situ PCR