The first component to consider in a PCR platform is the thermal engine. Successful thermal cycling is dependent on the accurate regulation of temperature in the sample vessels and the speed at which these target temperatures can be achieved. The majority of real-time platforms use advanced heating block technology based on the Peltier-effect, to actively transfer heat in and out of thin-walled plastic reaction vessels (e.g. ABI 7300, ABI 7500, ABI 7900HT, ABI Step One, Opticon 2, MiniOpticon, Chromo 4, Mx4000, Mx3000P, Mx3005P, Mastercycler ep, MyiQ, iQ5, LightCycler 480).

Peltier devices transfer heat from one side of a semiconductor to another. In general, blocks have significant mass and consequently a degree of thermal inertia. Furthermore, the plastic insulating layer between the reaction vessel and the heater produces an additional thermal lag. As a consequence of this, the temperature transitions are relatively slow and blocks must be very carefully designed to minimise well-to-well variation. Other advances on the Peltier-based technology include its combination with Joule, resistive or convective technology to give improved temperature control and performance across the block.

More recently has been the inclusion of patented Therma-Base technology, whose working principle is based on the evaporation and condensation of a working fluid in a thin vacuum cavity to accurately control well-to-well variation. Three platforms employ alternative heat exchange technologies which permit more rapid thermal ramp rates than blocks, resulting in significantly increased thermocycling speeds. These include a stationary turbulent air-heated glass capillary format (LightCyclers 1.5 and 2.0), a centrifugal air-heated plastic tube format (Rotor-Gene) and a high-thermal-conductivity ceramic heating plate plastic tube format (SmartCycler). For example, the time taken to equilibrate at 72°C using a Rotor-Gene is 0s compared to 15s with a standard 96-well peltier block, resulting in run times that are on average 50% faster. A recently published review (Logan and Edwards 2009) indicates that the LightCyclers 1.5 and 2.0 have the capacity to perform the fastest PCR and the Rotor-Gene has the smallest variation in temperature uniformity.

from Logan and Edwards (2009) in Real-Time PCR: Current Technology and Applications

Bibliography:

1. Real-Time PCR: Current Technology and Applications
2. Real-Time PCR in Microbiology: From Diagnosis to Characterization
3. PCR Troubleshooting: The Essential Guide
4. PCR Books

Labels: heating block technology, PCR platform, Therma-Base technology, thermal cycling, thermal engine, thermocycling