The unit performs reliably, is menu driven for programming various PCR (Polymerase Chain Reaction) "recipes" (so you don't have to use a computer but there is free downloadable software that will let you do this and we provide the PIN diagram for making the cable). It cycles temperatures at 0.15 degree centigrade per minute. The difference in actual temperature (Process variable) from "control" temperature (Set variable) varies about 5 degree centigrade. That means we set the temperature at 5 degrees higher than the temperature we want to achieve. This is due to the bias in the thermocouple probe.
In a Nutshell: We use a piece of aluminum rod, drill a 1/4" hole in the center of one end for a cartridge heater and another hole near the rim of the same end for a thermocouple (temperature sensor). Additional holes in the same end of the rod are for sample tubes (0.2 ml eppendorf tubes).
This "heating block" is positioned on a small bracket over a PC cooling fan. Both are placed inside of a metal coffee cup. A commercial temperature controller ( available from Omega Engineering) is used to control the heating and cooling cycles. End of story.
It reaches and holds (soaks) at various temperatures and can also be used for "In situ" Hybridization protocols. It can be programmed from the face plate of the controller or connected to a computer by a serial cable. The control software is a free download.
Step 1: What is a Thermocycler?
A thermocycler raises and lowers temperature. For molecular or DNA applications it needs to heat up to about 90-95 degrees centigrade. DNA which usually exists in double strands in a helix (like a spiral staircase) and at about 92 degrees centigrade the strands will break and fall apart.
The solution that the DNA sample is in has extra "bases" that will connect to the broken rungs of the ladder to make two new ladders. To do this part we need to cool down the sample to the point where "bases" can connect to the separated DNA strands. If you cycle through this temperature range from 20-30 times you can make millions of copies of the original DNA.
So in summary, a thermocycler can make a million copies of one original piece of DNA. These copies can then be used for other types of research. The prototype that we build can take 6 sample tubes (0.2 ml eppendorf tubes). There is room for one blank, the temperature probe and a central cartridge heater.
Learning sites that are excellent:
- DNA Extraction Online Tutorial
- Home DNA extarction of DNA (Instructables)
- PCR Song (must hear)
- PCR Protocols