PCR

The Polymerase Chain Reaction (PCR) is a well-known technique for the selective amplification of specific DNA sequences. The use of this method allows a small quantity of DNA material to produce a large number of target sequences, increasing the probability to have correct detection results. For this reason, PCR has become one of the most widely used techniques in molecular biology.

The PCR technique requires the preparation of a reaction mixture containing the DNA template for amplification and other reagents. The sample must then be heated and cooled according to the thermal cycle of the reaction protocol. A typical protocol consists of a three-step cycle (95ºC, 55ºC, 72ºC)which is repeated 30-35 times.

A single PCR cycle doubles the original concentration of DNA. Repeating the thermal cycle thirty times results in an amplification factor of 2^30, thereby producing about 1 billion times the original concentration of DNA. Although the amplification factor achieved under real experimental conditions is always lower than the theoretical one, PCR is still an effective way to amplify the concentration of a desired DNA sequence. In most cases, 20 to 40 PCR cycles will produce a sufficient quantity of DNA.

PCR is generally executed using programmable instruments called thermocyclers.
Although they represent a reliable way to perform the reaction, the growing interest for integrated assays (e.g. the "lab-on-a-chip" project) has encouraged researchers to develop alternative devices.
PCR biochips are miniature devices that operate by using smaller samples of genetic material. This reduces both the costs and the time required for a reaction. The integration of these devices in more complex systems is the first step in the creation of device for automatic genetic assays.