Colloidal gold is a commonly used labeling technology, which is a new type of immunolabeling technology using colloidal gold as a tracking marker applied to antigens and antibodies, with its unique advantages. It has been widely used in various biological researches in recent years. Almost all clinical immunoblotting technologies use its labels. It can also be used in flow, electron microscopy, immunology, molecular biology, and even biochips.
In 1971, colloidal gold was introduced into immunology, and since then, the immunological colloidal gold technology has been widely used in various biomedical fields as a new immunological testing. In medical testing, the application of colloidal gold is mainly in immunochromatography and rapid immunogold filtration. It is used to detect HBsAg, HCG, and anti-double-stranded DNA antibodies, and has the advantages of being simple, fast, accurate, and pollution-free.
Colloidal gold is formed by polying gold particles of a certain size by chloroauric acid under the action of reducing agents such as white phosphorus, ascorbic acid, sodium citrate, and tannic acid, and then it forms a stable colloidal state due to electrostatic effect, forming a negatively charged hydrophobic colloidal solution. Because of this electrostatic effect, it is called colloidal gold. Colloidal gold carries a negative charge in weakly alkaline environments and can form a firm bond with positively charged groups of protein molecules. As this bond is an electrostatic bond, it does not affect the biological properties of the protein.
In addition to binding to proteins, colloidal gold can also bind to many other biopolymers, such as SPA, PHA, ConA, etc. According to some physical characteristics of colloidal gold, such as high electron density, particle size, shape, and color reaction, combined with the immune and biological characteristics of the binding materials, colloidal gold has been widely used in immunology, histology, pathology, and cell biology.
The labeling of colloidal gold basically refers to the process of protein and other high polymers being adsorbed onto the surface of colloidal gold particles. The adsorption mechanism may be that the negatively charged surface of colloidal gold particles binds firmly with the positively charged groups of proteins due to electrostatic adsorption. Reduction testings can be used to conveniently prepare colloidal gold particles of various sizes or colors from chloroauric acid. These spherical particles have strong adsorption functionality to proteins and can non-covalently bind with many materials such as Staphylococcus A protein, immunoglobulin, toxin, glycoprotein, enzyme, antibiotic, hormone, bovine serum albumin peptide conjugates, etc., making them very useful tools in basic research and clinical trials.
The immunogold labeling technology mainly utilizes the high electron density of gold particles. Black or brown particles can be seen at the gold-protein binding site under a microscope. When these markers are heavily aggregated at the corresponding ligand site, red or pink spots can be seen with the naked eye. Therefore, in qualitative or semi-quantitative rapid immunodetection testings, this reaction can also be amplified by silver particle deposition, which is called immunogold-silver staining.