Structural characteristics of colloidal gold and commonly used detection techniques
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Update time : 2020-04-13 16:45:21
(1) The structure of colloidal gold Colloidal gold, also known as gold sol, is a suspension of gold particles formed after the gold salt is reduced to the original gold. The colloidal gold particles are composed of an essential gold core (atomic gold Au) and a double ion layer surrounded by it. The inner layer of negative ions (AuC12-) is connected to the surface of the gold core, and the outer ion layer H + is dispersed in the solution between the colloids to maintain the suspension state of colloidal gold free between sols. The primary gold core of colloidal gold particles is not an ideal spherical core. The smaller colloidal gold particles are basically spherical, and the larger colloidal gold particles (generally refers to those more significant than 30 nm) are mostly elliptical. The particle morphology of colloidal gold can be observed under an electron microscope. (2) Characteristics of colloidal gold 1. Colloidal nature The size of colloidal gold particles is mostly in the range of 1-100 nm. The tiny gold particles are suspended in the liquid stably, uniformly, and in a single dispersed state to become a colloidal gold solution. Colloidal gold thus has various properties of colloids, especially sensitivity to electrolytes. The electrolyte can destroy the permanent hydration layer of the colloidal gold particles, thereby breaking the stable state of the colloid, and causing the dispersed single gold particles to condense into massive particles and precipitate from the liquid. Certain macromolecular substances such as proteins have the effect of protecting colloidal gold and enhancing its stability. Colloidal gold is a commonly used labeling technology. It is a new type of immunolabeling technology that uses colloidal gold as a tracer marker for antigens and antibodies. It has unique advantages. In recent years, it has been widely used in various biological studies. Almost all immunoblotting techniques used clinically use their label. At the same time, it can be used in flow cytometry, electron microscopy, immunology, molecular biology, and even biochips. Colloidal gold is made of chloroauric acid (HAuCl4) under the action of reducing agents such as white phosphorus, ascorbic acid, sodium citrate, tannic acid, etc., and can be polymerized into gold particles of a specific size, and it becomes a stable colloidal state due to static electricity. Forming a negatively charged hydrophobic glue solution, it becomes a steady colloidal state due to static electricity, so it is called colloidal gold. Colloidal gold is negatively charged in a weak alkaline environment and can form a strong bond with the positively charged groups of protein molecules. Because this bond is electrostatic, it does not affect the biological characteristics of the protein. Colloidal gold labeling is essentially a coating process in which proteins such as proteins are adsorbed onto the surface of colloidal gold particles. The adsorption mechanism may be the negative charge on the surface of the colloidal gold particles, which forms a strong bond with the positively charged groups of the protein due to electrostatic adsorption. Colloidal gold particles of various particle sizes, that is, different colors, can be easily prepared from chloroauric acid by reduction method. This spherical particle has a healthy adsorption function for proteins. It can be non-covalently combined with staphylococcal protein A, immunoglobulins, toxins, glycoproteins, enzymes, antibiotics, hormones, bovine serum albumin polypeptide conjugates. Therefore, it has become a handy tool in basic research and clinical experiments. Common detection technology Immunocolloid gold staining Cell suspension smears or tissue sections can be stained with colloidal gold-labeled antibodies or can be enhanced with the silver developer based on colloidal gold labels, so that the reduced silver atoms are deposited on the surface of the labeled gold particles Can significantly enhance the sensitivity of colloidal gold labeling. Immunocolloid gold electron microscope staining Antibodies or anti-antibodies labeled with colloidal gold can be combined with negatively stained virus samples or ultrathin sections of tissues, and then negatively stained. It can be used for the observation of virus morphology and virus detection. Dot immunogold filtration Use a microporous membrane (such as a membrane) as a carrier, first spot the antigen or antibody on the layer, add the sample to be tested after sealing, and wash it with colloidal gold-labeled antibody to detect the corresponding antigen or antibody. Colloidal gold immunochromatography The specific antigen or antibody is fixed on the membrane in a stripe shape, and the colloidal gold labeling reagent (antibody or monoclonal antibody) is adsorbed on the binding pad. When the sample to be tested is added to the sample pad at the end of the test strip, it passes the capillary action Move forward, dissolve the colloidal gold labeling reagent on the binding pad, react with each other, and then move to the area of fixed antigen or antibody, the conjugate of the test substance and the gold labeling reagent will specifically bind to it and be trapped and aggregated. The color development results can be observed with the naked eye on the test strip. The method has now been developed into a diagnostic test strip, which is very convenient to use. Rapid gold standard reagent technology The specific antibody is first fixed to a particular zone of the acid cellulose membrane. When one end of the dried acid cellulose is immersed in the sample (urine or serum), the sample will move forward along the membrane due to capillary action Move, when moving to the area where the antibody is fixed, the corresponding antigen in the sample will specifically bind to the antibody. At the same time, the use of gold particles has the characteristics of high electron density at the junction of gold-labeled proteins. When these markers aggregated in large amounts at the corresponding ligands, red spots were visible to the naked eye. It is the principle of the rapid gold label detection method. The production of fast and precise reagents depends on whether the sensitivity and specificity of the materials used, such as monoclonal antibodies, polyclonal antibodies, antigens, haptens, protein chimeras, and colloidal gold can reach the highest standards. This is gold The most crucial standard for the quality of standard reagents.
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