Can orange juice coke show Yang? Antigen detection operation needs to be standardized
2022-04-29
Recently, a wave of odd operations of brain holes caused onlookers—— Drop orange juice or coke into the small hole of the new crown antigen detection board, and the test results can even show "two lines"... There are rumors that eating oranges and drinking Coke will affect the test results, and some netizens call directly. Is it too easy to get a false positive. However, from the perspective of R & D personnel, these so-called "false positives" are completely out of thin air. "In the final analysis, any test product should be used according to the instructions if it wants to get the exact results. This is a basic common sense." Xu Lei, the R & D director of YingYuan zhongflux of Huada, told the science and Technology Daily that although some antigen detection products have gone out of the laboratory, the link of detection and verification is a rigorous scientific operation in the final analysis. Why can orange juice and coke show Yang Professor Zhu Yuqing found that the above-mentioned clinical test kits were invalid, and some of them were able to be tested by the Shanghai clinical laboratory; Some kits will be "hoodwinked", the quality control line is normal and displays weak positive. The reason is that different substrate components are used in the approved antigen kit. So why do orange juice and coke make some antigen tests false positive? The real positive color development is because the antigen detection captures the protein of the virus, the reaction of antibody binding to the virus protein occurs at the detection line, and the color development reaction is stimulated. Both the quality control line and the detection line are colored. Orange juice and coke can also color the detection line because the two acidic solutions directly stimulate the color reaction, so that the color can be developed without the presence of virus protein. In chemical reactions, the pH value in the solution system is very important, which determines the dissociation and binding of ions. Imagine that adding white vinegar to hot milk in daily life will lead to flocculent precipitation. It is not difficult to understand the protein denaturation caused by pH value (the antibody bound to the detection plate is also a protein). Due to the change of pH, the chemical structure is changed, which leads to the further occurrence of its color reaction and false positive. Zhu Yuqing explained in his popular science article: dropping orange juice directly into the reagent strip, the pH value of the solution is too low, and there is vitamin C in the orange juice. A large amount of reducing agent is easy to lead to abnormal aggregation of chloroauric acid colloidal gold, precipitation of some colloidal gold, and false positive report. In the design of the kit, there is a special design to avoid the change of pH value, that is, buffer solution. This solution acts as a "buffer" for a small amount of pH fluctuation caused by sweat and air, so as to avoid drastic changes caused by small changes in the whole reaction system and then affect the results. Even so, the buffer solution can not "buffer" the destructive impact on the whole experimental results caused by the addition of a large number of artificial acidic substances. Reject false positives, and see the trick for antigen detection For the convenience of detection, the antigen antibody reaction and color reaction are agglutinated on a thin detection plate. However, due to the physical adsorption of colloidal gold immunochromatography technology, the antigen / antibody is easy to separate from the surface of gold particles and the marker is unstable, which leads to the change of reaction environment and false positive of orange juice and cola. As of April 27, the State Food and drug administration has approved 30 novel coronavirus antigen detection reagent products. The detection principle of all approved products can be divided into three methods: latex method, colloidal gold method and fluorescence immunochromatography. The principle of the three methods is double anti sandwich method, but the color signals are different. The signal of colloidal gold method is nano gold particles, which is the color signal of visible light, which can be observed by the naked eye; Latex method is the result of naked eye observation with color source coated and also visible light; The signal substance of fluorescence immunochromatography is fluorescent substance, which needs to be given appropriate excitation light to emit corresponding fluorescence. Therefore, specific instruments are usually required to observe the detection results. However, fluorescent substance is more stable than colloidal gold and is suitable for semi quantitative detection, so the sensitivity of fluorescence immunochromatography is higher than the first two. "The color signal is more stable, which will avoid the occurrence of false positives caused by some operations contrary to the standard." Xu Lei said that in order to increase the stability of color signal, Huada's antigen detection products use nano microspheres as carrier technology and fluorescent marker probes to greatly improve the stability of color development in terms of carrier and luminescence. In addition, the detection signal does not rely on visual observation, but is quantified by fluorescence recognition equipment. Therefore, the information provided is more diagnostic value, and the sensitivity is about 10 times higher than that of traditional colloidal gold chromatography. It can be seen that antigen detection is not easy to be "false positive". Obviously, the operation is out of line. Don't let oranges and coke carry the pot again. (outlook new era)
Edit：Yuanqi Tang Responsible editor：Xiao Yu
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