What are the types of PCR instruments and how to choose them?

Classification is always varied. Generally speaking, it can be divided into two categories: PCR amplification instrument and real-time fluorescence PCR instrument. Some people also call it semi-automatic and fully automatic, or qualitative and quantitative. These are inaccurate names.

The most important thing in PCR is the process of heating and cooling. The original water bath PCR consists of three water bath boxes and a mechanical arm, and the reaction tank is taken out regularly and replaced with a water bath pot. This thing is big, fast and slow, but in fact, the result is not worse than the later PCR instrument, and I appreciate it now. Later, someone used the method of refrigeration and heating to make a PCR amplifier with fixed temperature rise and fall.

Later, with the development of quantitative technology, some companies integrated the amplification instrument with detection and became the so-called automatic (or quantitative) PCR instrument. Of course, the standard is called real-time fluorescence quantitative PCR instrument.

brand

Everything has a brand. Now there are many brands of PCR instruments at home and abroad. As far as foreign countries are concerned, the famous ones are:

ABI American Applied Biology Company: a noble old biological company, bought original PE. PE Company is the originator of PCR, and has many classic PCR instruments, including 5700 (discontinued), 7700 (discontinued), 7000, 7900 and other real-time fluorescence quantitative PCR instruments.

Roche Roche's diagnosis: the hot upstart LIGHTCYCLER is its only PCR instrument. The market is doing well, focusing on scientific research. But many hospitals in China are using it. It is the most unique PCR instrument with unique centrifugal, gas heating and capillary design. Of course, quality is another matter, so its unique technical ability and courage are admirable.

MJ: A celebrity who just entered China, MJ's amplifier is very famous in the field of life science research. Its products are suitable for quantitative detection in Qualcomm and widely used in human genome project. In fact, the real-time fluorescence PCR instrument has just entered China, and its characteristic is that it can use different temperatures between wells. This is actually more useful.

Bole: Ah, cheap McDonald's, ICYCLER is its main product. It's been a long time in China. Like the 5700, the product adds a quantitative module to the amplifier, which is characterized by lower price.

There are also many projects in China, such as Boli in Hangzhou, Ji Lang in Hangzhou, Fengling in Shanghai and Ampley in Xiamen.

Selection and purchase

Accurately speaking, there is no automatic sampling and sample processing system, including real-time fluorescence quantification, which can only be regarded as semi-automatic. The PCR instrument is a simple thing, a temperature control device and a detection device.

Regarding temperature control, the main problem is the medium. The ideal medium is something with good thermal conductivity, large specific heat and close contact.

The best in this respect are water bath and oil bath, which have high specific heat (oil is greater than water), the object is solvated, and the contact with reactants is seamless, and the effect is of course the best. However, automation and miniaturization are difficult, and only the initial water bath pot type is adopted.

Silicon heating is the most commonly used one, which has the advantages of easy automation, high speed, direct heating and cooling, good effect and so on, but the first cost is high. Secondly, the medium used is metal, which has good thermal conductivity, but it is difficult to contact the reaction tube seamlessly. When qualitative, you can add oil, but you can set the temperature by fluorescence, because oil has fluorescence signal, so it can't be used. It is worse in seamless contact. Thirdly, because it is heated at the bottom, the pressure at the lower part is high, which may overflow, but the new instrument solves this problem after heating the cover.

Air heating, with air as the medium, has the advantage of seamless contact with the reaction system, but air has the obvious weakness of poor thermal conductivity and small specific heat. Therefore, air heating should make use of air flow generated by centrifugation to enhance thermal conductivity, and at the same time, capillary tubes should be used to increase contact area and trace reagents to make up for it. After doing this, the effect is still good. However, some manufacturers talk about the advantages of centrifugation and capillary, but keep silent about the weakness of gas heating, which is a clever market technique. At the same time, the use of centrifugation has an impact on the increase of sample size. The larger the sample size, the more obvious the weakness of low specific heat of air, so the sample size of air heating instruments is relatively small. After the capillary tube is used, the contact area between the reaction liquid and the tube increases, and the adsorption phenomenon is greater. Therefore, the reagent has poor universality and high cost. Although the dosage of reagents is small, because they are special reagents, each reagent is calculated according to the actual dosage, which does not save reagents. But increase that cost of the capillary tube.

With regard to functions, all PCR instruments are basically the same. The only difference is that only MJ holes can use different temperatures, which is useful for simultaneously detecting multiple items and adjusting cycle parameters. However, the real-time fluorometer has just entered China, and the specific situation is still unknown.

Regarding the purchase, it depends on the company. Because the technical content of PCR is actually not high, good domestic instruments such as Hangzhou Bori (related to the famous Japanese manufacturer Daiwa) are not too bad. As for imported instruments, Roche's instruments are good, but if the number of specimens is large, it is recommended not to use Roche. One will be exhausted. In addition, the cost of standard curve and control shared by each sample is too high. At the same time, the reagents are limited.