Lateral flow test What is the principle of the colloidal gold test method?

Colloidal gold can be polymerized into gold particles of a certain size by chloroauric acid (HAuCl4) under the action of reducing agents such as white phosphorus, ascorbic acid, sodium citrate, tannic acid, etc., and become a stable colloidal state due to electrostatic interaction. It forms a negatively charged hydrophobic colloidal solution, which becomes a stable colloidal state due to electrostatic interaction, so it is called colloidal gold. Colloidal gold is negatively charged in a weak alkaline environment and can form a firm bond with the positively charged groups of protein molecules. Since this bond is electrostatic, it does not affect the biological characteristics of the protein.

In addition to binding to proteins, colloidal gold can also bind to many other biomacromolecules, such as SPA, PHA, ConA, etc.

Because colloidal gold has this characteristic, it is often used for detection, so it has become a detection method, named after the colloidal gold method. for example

Principle of morphine detection test paper (colloidal gold method): This product adopts colloidal gold immunochromatography technology, coats morphine antigen on nitrocellulose membrane, and coats specific antibody labeled with colloidal gold on glass fiber. During detection, if there is no morphine or its metabolites in the sample, the colloidal gold-labeled specific antibody combines with the membrane region antigen to form two red lines (one reaction line T, one quality control line C), indicating that the test result is negative; If there is morphine or its metabolites in the sample, and the concentration is higher than the detection level (300ng/ml), the drug molecule will compete with the colloidal gold-labeled antibody for binding, thereby preventing the colloidal gold-labeled antibody from binding to the membrane region antigen, making it The corresponding red reaction line disappears, and only a red quality control line appears, indicating that the test result is positive.