Colloidal gold is a commonly used labeling technique; in addition, it is also an antigen/antibody immuno-labelling technique that selects colloidal gold as a tracing marker. In 1971, Faulk and Taytor introduced colloidal gold into immunochemistry. Since then, the immune colloidal gold technique, as a new immunological method, has been increasingly applied in various fields of biomedicine. Its major applications in medical examination include immunochromatography and dot-immuogold filtration assay (DIGFA). Being simple, rapid, accurate and pollution-free, etc., it is used to detect HBsAg, HCG and anti-double strand DNA antibody, etc.
Structurally, a colloidal gold detection product is primarily composed of a sample pad, a colloidal gold bonding pad, a detection line, a quality control line and a liner. Regarding major principle, it can be described as follows. Under capillary actions, test samples, test conjugates, antigens for the detection line and antibody fixation can be guided directionally; in this way, it can be determined whether the sample contains any target material (qualitative detection) or specific content of such target material can be identified (quantitative detection).

1、Immunocolloidal gold staining based on light microscope ：Cell suspension smears or tissue sections can be stained by colloidal gold labeled antibodies; alternatively, silver developer can be adopted to enhance the marker based on colloidal gold labeling, so that the reduced silver atoms deposit on the surface of labeled gold particles; in this way, sensitivity of colloidal gold markers are significantly improved.
2、Immunocolloidal gold staining based on electron microscope：The colloidal gold labeled antibodies or antiantibodies may bind to negatively stained virus samples or ultrathin tissue sections; after that, negative staining is carried out. Moreover, such an approach can be performed to observe virus morphology and detect viruses.
3、Dot-immunogold filtration assay：A millipore filter (e.g., membrane) is selected as the vector. Firstly, antigens or antibodies are dotted on the filter and then closed; secondly, the specimen to be detected is added; after washing, the colloidal gold labeled antibodies are used to detect corresponding antigens or antibodies.
4、Colloidal gold immunochromatography：Specific antigens or antibodies in a stripped shape are fixed on the filter; and, colloidal gold labeling reagent (antibodies or monoclonal antibodies) are adsorbed on the conjugate pad. Once the test sample has been added on a sample pad at one end of the test strip, it moves forward under the capillary action, so that colloidal gold labeling reagent on the conjugate pad is dissolved and mutually react with it; subsequently, when it moves to an area of the fixed antigens or antibodies, it is entrapped because of specific binding that takes place between it and conjugates of the test substance and the colloidal gold reagent; as a result, the test sample is accumulated on the test strip and the corresponding staining outcome can be observed by naked eyes. Now, diagnostic strips of convenient use have been developed based on such a method.
5、Rapid colloidal gold reagent detection method：Specific antibodies are firstly fixed on a zone of acid cellulose membrane. Once an end of the dry acid cellulose is immersed into the sample (urine or serum), the sample moves forward along the membrane due to a capillary action; when it moves to the zone where the antibodies are fixed, specific binding takes place between corresponding antigens in the sample and the antibodies. Meanwhile, considering a high electron density feature of gold particles, red dots become visible to naked eyes at a position where colloidal gold proteins bind to each other under the circumstance that these markers extensively accumulate at relevant ligands. This is the principle of rapid colloidal gold reagent detection method. The key to producing rapid and precise reagent lies in the fact whether sensitivity and specificity of raw materials such as monoclonal antibodies, polyclonal antibodies, antigens, haptens, chimeric substances of proteins, and colloidal gold meet the highest standards. This is the most important criterion for colloidal gold reagent reagent.

According to the fact whether a detecting device is required, the methods consist of interpretation by naked eyes and instrument respectively. The basic procedures are rather simple and easy of operation, including addition of sample, reacting and result interpretation. Moreover, interpretation by instrument provides quantized data. At present, the assorted detecting instrument has been miniaturized, networked and provided with a user-friendly interface. On this basis, on-site real-time detection and remote data transmission are realized.

On the existing nano immune process platform, we succeed in developing and preparing colloidal gold immunochromatograohic assay and rapid colloidal gold immunity filtration assay products. It can be used for detection in the fields of life sciences, animal medicine and public safety, etc.. The platform has the following characteristics:
1、The established standardized nano-immunochromatography card production platform which conforms to GMP criteria. It is applicable to automated and standardized production.
2、The platform is featured with a stable and mature production process system and a good quality management system, accumulation of rich experience in nano-detection technology development, and possessing a highly professional technical team.
3、It possesses the capability to independently develop key raw materials, which ensures stability and optimization of product performance.
4、In addition to techniques and processes that adapt to nano-immunochromatography cards, we also develop a dual-mode chart reader for colloidal gold immunochromatography cards/fluorescent immunochromatography cards. Therefore, not only can on-site detection be carried out, but detection results can be quantitatively read. In addition, it is also provided with other functions such as instant printing and remote data transmission.
5、The developed products are featured with sensitivity, specificity, convenience and rapidness, etc.. Stored in an ambient temperature, such products possess a period of validity up to 18 months.