II-VI Marlow

PCR and the Role of Thermoelectrics in Temperature Cycling

This entry was posted in Thermoelectrics and PCR on July 08, 2016 by II-VI Marlow Industries

The polymerase chain reaction (PCR) is a technology in molecular biology used to amplify a single copy, or a few copies, of a piece of DNA across several orders of magnitude, generating thousands to millions of copies of a particular DNA sequence.

Thermoelectrics Achieve the Temperature Cycling Required in Polymer Chain Reaction (PCR)

PCR relies on thermal cycling, consisting of repeated cycles of heating and cooling of the reaction block (a holding device) which contains DNA strands and primers (short DNA fragments).  A typical cycle with temperatures is shown in the graph below. 

temp_cycle_time

The temperature cycles required by this process are typically achieved through the use of thermoelectrics, which can both heat and cool.  PCR cycling is one of the most technically challenging thermoelectric applications.  The repeated temperature cycles create reliability challenges for the module, due to coefficient of thermal expansion (CTE) stresses.

II-VI Marlow has designed specific product lines to address PCR cycling.  We have been supplying thermoelectric modules and thermoelectric systems to support thermocycler production for over 20 years.  Our product line offering for thermocyclers has two types of products available, the XLT and LCC line of products.

Development of reliability testing to verify the performance of thermocyclers has been a key to our success in this market.  In the II-VI Marlow accelerated test cycle, the thermoelectric modules (TEMs) are epoxied to an aluminum heat sink.  The thermal mass of a typical heatload is removed in order to accelerate the cycling ramp rate.  Power is constantly applied to the TEMs.  When the TEMs reach the upper limit cycle temperature (95οC), the voltage polarity is reversed and the temperature of the topside reverses direction until it reaches the lower limit temperature (15οC).  Individual Alternating Current Resistance (ACR) measurements on each TEM are made periodically to monitor the life of the TEMs.  A photo of the test setup is shown below:

test_setup

An example of the test results on one part is shown in the chart below.  Ten modules were tested over the typical temperature range of 15-95-15οC.  The change in (ACR) was less than 2% after 450,000 test cycles.  These results meet and exceed the requirements of the cycling market.

accelerated_dna_cycling

The PCR market presents unique technical challenges and requirements for thermocycler product designers and manufacturer’s.  II-VI Marlow is well suited to accept those challenges head on!

II-VI Marlow has demonstrated market experience and product offerings that meet and exceed our customer requirements. Contact us today to learn more!

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