Colloidal gold immunochromatography (GICA) refers to a rapid solid-phase membrane immunoassay technique that uses a combination of colloidal gold labeling technology, immunodetection technology, and protein chromatography technology using nitrocellulose membrane as a carrier.
The principle is to use nitrocellulose membrane as a solid phase carrier, and the sample solution swims on the chromatography strip by capillary action; at the same time, the sample in the sample and the chromatographic material are directed to the receptor of the sample (such as antibody or antigen) . An immune reaction with high specificity and high affinity occurs. During the chromatography process, the immune complexes are enriched or trapped in a certain area (detection zone) of the chromatography material. The colloidal gold particles can be directly visually inspected in a short time. (Within 5 ~ 10min) gather and get intuitive experimental results.
It does not need to separate the binding label from the free label, so there is no such complicated loading and washing steps as in the Elisa experiment. This technology has the characteristics of simple and fast operation, the test results are clear and intuitive, and no special instruments (or only simple instruments) are needed, which is especially suitable for rapid on-site testing. Gold-labeled colloidal gold immunochromatography is divided into two categories according to the molecular size of the analyte: double-antibody sandwich method and competition method. The double-antibody sandwich method is suitable for the detection of large molecular substances, and has the characteristics of strong intuitiveness and high sensitivity, while the competition method is suitable for the detection of small molecular substances.
With the large-scale and intensive development of China's breeding industry, the harm of animal infectious diseases to the breeding industry is gradually increasing. Therefore, how to achieve rapid detection in order to prevent and control in time has become a key link. The appearance of gold standard colloidal gold chromatography technology makes rapid on-site detection possible.
Colloidal gold also known as nano gold, is a suspension of gold particles formed after the gold salt is reduced to the original gold. The colloidal gold particles are composed of a basic gold core (atomic gold Au) and a double ion layer surrounded by the outer layer. The inner layer of negative ions (AuC12-) is connected to the surface of the gold core. , To maintain the suspension state of colloidal gold free between sols. Generally, the colloidal gold particles below 30 nm are basically spherical, and the larger colloidal gold particles are mostly elliptical.
We provide colloidal gold particles ranging in size from 10 nm to 80 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 large particles and precipitate from the liquid. Certain macromolecular substances such as proteins have the effect of protecting colloidal gold and enhancing its stability.
The color of colloidal gold is another topic that everyone is concerned about. Generally speaking, colloidal gold colloidal products are the color of deep "red wine" or close to purple like other gold colloidal products. When concentrated x10, it is pale straw or brown. In fact, there are certain differences in the coloration of colloids of different sizes. The smallest colloidal gold (2-5 nm) is orange-yellow, the medium-sized colloidal gold (10-20 nm) is burgundy, and the larger-particle colloidal gold (30-80 nm) is purple-red.
Colloidal gold has a single light absorption peak in the visible light range. The wavelength (λmax) of this light absorption peak is in the range of 510-550nm, which varies with the size of the colloidal gold particles. The λmax of colloidal gold tends to be shorter wavelength.
The preparation of colloidal gold mostly uses the reduction method. Chloroauric acid (HauC14) is the main reducing material. Commonly used reducing agents are sodium citrate, tannic acid, ascorbic acid, white phosphorus, sodium borohydride, etc. Depending on the type of reducing agent and the strength of the reduction, colloidal gold ranging from 0.8 nm to 150 nm can be prepared. The most commonly used preparation method is the citrate reduction method.