For IVD analytical instruments, one of the indicators that must be mentioned in evaluating the fluid system is cross-contamination.

Cross-contamination, as the name implies, is when certain substances between the reactants are carried and crossed, causing substances that do not belong to this reaction to be brought into this reaction. The most direct impact of cross-contamination of instruments is to lead to inaccurate results, which in turn affects the accuracy of test reports and may lead to misdiagnosis in serious cases. Throughout the entire reaction process, according to the different sources of cross-contamination, cross-contamination can be divided into the following types.

1. Cross-contamination between samples

Because the cleaning of the sampling system is not thorough after each sampling is completed, the substances in the previous or previous samples are brought into the next or subsequent samples to be tested, leading to the subsequent samples The result deviates from the true value.

2. Cross-contamination between reagents

Similarly, the cross-contamination between this room is similar. The cross-contamination between the reagents means that after the reagent filling is completed, the cleaning of the reagent filling system is not thorough, which leads to the substances in the previous one or several reagents being brought into the latter. In the first or last few reagents, this substance will affect the reaction process, so it will lead to the deviation of the test results.

3. Cross-contamination in the reaction process

During the reaction process, due to the incomplete cleaning of the reaction vessel and the stirring and mixing device in the process, the substances of the previous or previous reactions remained on the reaction vessel and the stirring and mixing device, and then were brought into the next Or in the next few reactions, it will affect the results of the subsequent reactions, causing the test results to deviate from the true value.

Compared with other causes of abnormal results in analytical instruments, the abnormal results caused by cross-contamination are not easy to detect, and it is difficult to establish a corresponding alarm and feedback mechanism, so it needs to be reduced as much as possible in the design side. To analyze the cause of cross-contamination, in the final analysis, it is still a problem of cleaning effect. To reduce the cross-contamination of instruments, we can start with the following aspects.

1. Rationally design the structure of the device in contact with the reactive substance

When designing the sample (reagent) needle, stirring rod, and reaction vessel, the interior should be as smooth as possible, and there should be no dead corners. Dead corners often lead to residues of reaction substances and are difficult to clean thoroughly.

When designing the sample (reagent) needle, try to ensure that the internal volume of the needle can completely cover the maximum volume of the reaction substance added, so as to avoid the reaction substance entering the pipeline when adding the sample (reagent), due to the passage between the pipeline and the needle. The joints are connected, and it is difficult to clean the joints thoroughly.

2. Improve the surface finish of the device in contact with the reactive substance

It is not difficult to imagine that the smoother the surface of the device, the better the cleaning effect and the less cross-contamination introduced during use. Common ways to improve the surface finish include precision polishing of needles and stirring rods, coating (Teflon) to improve surface finish, and precision injection molds with a higher finish to improve the surface finish of reaction vessels, etc.

3. Increase the flow rate of the cleaning solution

According to the knowledge of fluid mechanics, according to the Reynolds number, the cleaning effect of the fluid flow rate is poor in the steady flow state, and the cleaning effect is better in the turbulent flow state. Therefore, it is necessary to increase the flow rate of the cleaning liquid. There are two ways to increase the flow rate. When the flow rate is sufficient, reduce the inner diameter of the needle and the outlet of the cleaning pipeline, and increase the flow rate when the inner diameter remains unchanged. Of course, this puts higher demands on the pump. In practical application, a trade-off needs to be made between pump cost, water consumption, and cleaning effect.

4. Choose the right cleaning solution and temperature

Different cleaning solutions have different cleaning effects. Like the reagent formula, each manufacturer’s cleaning solution also has different formulas. It is necessary to develop a special cleaning solution according to the different characteristics of the manufacturer’s reagents.

Different temperatures of the cleaning liquid will also have different cleaning effects. Generally, a heating device is designed inside the instrument to heat the cleaning liquid to achieve a better cleaning effect.

5. Other ways to completely eliminate cross-contamination

For example, the disposable cuvette and disposable TIP head sampling method used by some instruments completely eliminate cross-contamination from the source. In recent years, some manufacturers have used ultrasonic stirring to mix and mix, without contact throughout the process, completely eliminating cross-contamination.

I believe that with the continuous advancement of technology, there will be more advanced and efficient ways to reduce cross-contamination in the future, we will wait and see.