How to choose a suitable nucleic acid extraction system, and what are the misunderstandings in the selection?

With the rapid development of biotechnology, with the application of PCR technology in various fields, including medical disease detection, agricultural genetic modification detection, and many other applications, high-throughput sample nucleic acid extraction has become extremely urgent, and many companies have launched With the automatic nucleic acid extraction instrument, there are various principles. How to choose a suitable nucleic acid automatic extraction instrument requires detailed analysis.

From the perspective of extraction principle, there are spin column method and magnetic bead method. The centrifugal column method automatic nucleic acid extraction system uses a centrifuge and an automatic pipetting device to combine the method. The throughput is generally 1-12 samples. The time is similar to manual extraction. It does not improve efficiency, and the price is not cheap. Not universal, suitable for labs with sufficient funds.

The magnetic bead method automatic nucleic acid extraction system is divided into the magnetic rod method and the suction method. First, the suction method. As the name suggests, the suction method is carried out by an automatic pipetting device, and the lysis solution and magnetic beads are added through the automatic pipetting device. Adsorption, aspirate the lysate, add the rinsing solution, magnetic bead adsorption, aspirate the rinsing solution, and add the elution buffer.

There seems to be no problem from the steps, but the biggest problem with the suction method is that in order not to remove the magnetic beads when removing the waste liquid, the pipette should not be too close to the magnetic beads to prevent the magnetic beads and the waste liquid from being sucked out. There is always a small part of the waste liquid that cannot be completely removed each time, especially the device with the magnet at the bottom. Because the magnetic beads are adsorbed to the bottom by the magnet, the pipette cannot be too close to the bottom, so that the rinsing solution cannot be completely removed. Removal, the residual salt and ethanol in the rinsing solution will affect the subsequent elution efficiency and PCR success rate; the magnet on the side of the device will have less residual liquid, but the elution efficiency is not good, relying on the DNA to dissolve to the wash. In the de-buffered solution, unless you wait for more than half an hour, so in some 96 automatic nucleic acid extraction workstations, the extraction-round time takes 150 minutes, and the 32-magnet method can take 5 rounds in the same time.

Let’s talk about the magnetic rod method nucleic acid extraction system. The flux usually has 8, 16, 32, 96 channels. Compared with the suction method, the advantage of the magnetic rod method is that the liquid in each step does not remain, because the magnetic rod only takes away the magnetic beads and transfers Go to the corresponding reaction well in the next step. In addition, the extraction instrument of the magnetic rod method should be more complete, such as heating, and each heating tank should be independently temperature controlled, so that heating, lysis, and elution can be set. Different temperatures, another very important point is that the motor that drives the magnetic rod must be able to drive the magnetic rod to quickly mix and stir the liquid, so as to facilitate automation and help lysis and rinsing thoroughly.

The flux selection of the magnetic bar method is best to choose 32 channels. The 96 channels seem to have higher flux, but there is a very practical problem. When 96 magnetic bars are transferred from one plate to another, the magnetic bars are on the top. What to do if the liquid drops halfway, it will drip into other holes and cause pollution, and the 32-channel magnetic rod does not pass through the sky above other samples, so there will be no cross-contamination.

The above is the relevant introduction about the selection of nucleic acid extraction system, but many people are still easy to fall into the misunderstanding of selection. The following examples illustrate the two most common misunderstandings:

Misunderstanding 1: The difference between nucleic acid extraction system and workstation and the misunderstanding of selection

Many workstation manufacturers often tell their customers when they promote their workstations that the nucleic acid extraction system is fully automatic, while the nucleic acid extraction system is semi-automatic. Customers also subjectively think that the workstation can pipette, extract, and do anything, as if just put the sample in. Go in, you can get the nucleic acid you want without worrying about anything. When the workstation is in place, it turns out that the actual situation is not that way. Not only is it not as good as expected, but even the basic nucleic acid extraction is difficult. So what is the reason? ?

The first question is the problem of opening the lid. The lid structures of blood collection tubes, saliva storage tubes, and two-dimensional code cryopreservation tubes are different, the sizes are different, and the manufacturers are different. How to open the lid automatically at the workstation? This problem is solved No more.

The second problem is the entry of barcodes, barcodes and QR codes, as well as some manually affixed labels and handwritten labels, so the scanning of codes is still manual, which is difficult to automate.

The third problem is that the liquid addition is automated. The workstation can automatically add reagents, which seems to be an advantage, but it takes about 15-30 minutes to add a 96 deep-well plate, and extraction generally requires six reagents, that is, six plates. It takes about 1.5 hours. Many extraction reagents contain high concentration of ethanol. For such a long time, the concentration of ethanol will change, which will affect the extraction efficiency and sensitivity. Besides, many extraction instrument manufacturers have pre-installed kits that do not need to be added. liquid.

Misunderstanding 2: The difference between imported and domestically produced, this is the biggest misunderstanding of choice

Many people choose a nucleic acid extraction system based on habitual thinking and think that imported ones are better than domestic ones; however, nucleic acid extractors are application-oriented equipment, not basic experimental equipment, not the kind of equipment that can be used when plugged in. Nucleic acid extraction requires the overall cooperation of instruments, supporting kits and application programs. Manufacturers need to select the most suitable extraction kits and procedures according to the sample type. Reagents and procedures often need to be optimized. Without the manufacturer’s technical support, you cannot use it. . This explains well why many imported workstations and extraction instruments are collectively used by no one; the technical support of imported instruments cannot keep up, and the technical visits of imported instruments require expensive door-to-door fees, and there is no guarantee that they can be used. Help customers optimize the experimental plan (of course, the door-to-door fee must be charged).

On the whole, most nucleic acid extraction systems cannot keep up with domestic manufacturers in terms of instrument operating system convenience, instrument extraction sensitivity and yield, instrument kits, instrument upgrade and customization capabilities, etc., and the after-sales service charges are even more frustrating. There is no need to demonstrate the superiority of imports. Through the above discussion, we should be clear that when choosing a nucleic acid extraction system, it is best to conduct full research or trial, so as not to fall into the passive situation of buying a nucleic acid extraction system.