In-Vitro Diagnosis (IVD) Test Kits

In-Vitro Diagnosis (IVD) refers to a series of assay methods, in which human blood, urine or secretion specimens etc. are tested outside of the human body, so as to find the clinical proof of certain health conditions such as virus infection, diseases, damage to certain organ.

Atlas Link Technology Co., Ltd is concentrated on the supplying of IVD reagent kits, and is supplying immunoassay and clinical chemistry products. Among them, the lateral flow assay kit, dot filtration assay kit and dot-ELISA kits are easy to use, and don't need extra equipment or reagent, and are suitable to be used as Point of Care Test (POCT) Kits; while ELISA kits are usually used in the clinical labs on a whole set of equipment.

The IVD kits that Atlas Link is supplying can be divided into 5 categories of IVD reagent kits, based on the related technology adopted. Introductions about these testing methods are given as follow.

  1. Gold Immuno-Chromatographic Assay (GICA)
  2. Dot Immuno Gold Filtration Assay (DIGFA)
  3. Dot Enzyme Linked Immunoadsorbent Assay (Dot ELISA)
  4. Enzyme Linked Immunoadsorbent Assay (ELISA)
  5. Enzyme Reaction Dry Chemical Colorimetric Assay
Picture of Lateral Flow immuno-assay

Lateral Flow rapid tests are one-step qualitative test devices, based on the immune-chromatographic principle. They are a simple device intended to detect the presence of a target analyte in the in-vitro samples, such as urine, serum, plasma, whole blood, swab specimen and saliva. These tests are usually used for medical diagnostics either for home self testing, point of care testing, or laboratory testing. The test kits may come in three formats, namely strip, cassette and midstream. But the core device is the membrane strip that contains reagents.

In the lateral flow test method, colloidal gold particle are usually used as the coloring material. They are conjugated with antibody or antigen, thus they will move together with the latter. This small nanometer size iron particles are very small, and can suspend in fluid. At a low concentration, the fluid shows no color. And when the concentration becomes higher, the fluid shows pink or red color. In a double sandwich lateral flow test, when there is target analyte in the specimen, the antibody-antigen immune-binding action is used to make the colloidal gold particle to congregate in the test band region, thus to show a pink or red color there. While in a competitive test, the present of the target analyte will hinder the congregation of the colloidal gold particles in the test band region, thus no color develops there. Although latex can also be used as the coloring material which shows blue color, our kits are all based on colloidal gold technology.

There is a trade-off between the time saving and the technical characters, such as sensitivity and specificity. While it is a quick testing or screening device, the testing result may seem not so accurate. With the positive results, it is always advisable to test the specimens with more complicated technologies such as PCR. And, clinical conclusion must not be reached by the physician after all clinical information is evaluated.

Dot Gold Filtration Immuno Assay (DGFIA)

The Dot Immuno-Gold Filtration Assay (DIGFA), developed from the Dot ELISA technology in the late twentieth century, is a new technique with the merit of simple and rapid immunological detection. At present, DIGFA is widely used to detect IgG and IgM antibodies in the medical diagnostic realm.

In the DIGFA test, the indicator is the colloidal gold conjugate, whose main component is colloidal gold particles labeled with a secondary antibody (Indirect method), or with recombinant or purified antigen (double antigen sandwich or capture method). The Millipore filtering membrane (usually nylon or nitrocellulose) is pre-coated with purified antigen or secondary antibody, which acts as capturer to bind and immobilize the target IgG or IgM antibody.

When the serum and gold conjugate are added in sequence, the antibody-antigen immuno interaction is finished in short time. If the target antibody present in the sample, the immuno complex will be bounded on the membrane, at whose end is the colloidal gold particles. These particles can show red or pink color to human naked eyes, indicating a positive result. The total assay process takes only minutes.

Dot ELSIA, is a technology developed from the traditional ELISA technology. It is a combination of an Enzyme linked immunoadsorbent Assay and the millipore filtration technology. As with all the immuno interaction based assay technology, the assay principle is still based on the interaction between antigens and their specific antibodies. Purified or recombinant antigens or secondary antibodies (anti-human IgM) are used as the capturer of the target IgG and IgM antibodies. This capturer is immobilized in the millipore filtering membrane (usually nylon or nitrocellulose) instead of the solid phase microplate of polystyrene or polyvinyl chloride. Because it is much easier for the antibody or antigen to adhere to the nitrocellulose membrane, the production process of the test kit gets more efficient; and because the filtration effect can effectively reduce the interaction time between the antibodies and antigens, the assay time is reduced significantly. As a result, the dot ELISA technology is rapidly adopted in the medical diagnostic realm.

The main difference between DIGFA kit and Dot ELSIA is the indicating technology. In dot ELISA assay, the develop of the indicating color is developed by adding the substrate such as Tetramethyl benzidine (TMB) and urea peroxide, which are hydrolyzed and show certain visually detectable colors. While in DIGFA, the color is naturally developed by the physical congregation of the colloidal gold particles.


ELISA, short for Enzyme-linked Immunosorbent Assays, is immunochemical methods for determination of substances such as antibodies and viral antigens, or other proteins or peptides. ELISA combines the natural specificity of antibodies and the sensitivity of the simple enzyme assay, in which the pivotal reaction in the process of detection is the antigen-antibody interaction. ELISA kits are done in micro-titer plates made of polystyrene or polyvinyl chloride. These assays also utilize antibodies or antigens that are conjugated to an enzyme (usually horseradish Peroxidase, HRP). This enzyme can catalyze an easily visualized reaction, such as a color change, when substrate such as Tetramethyl benzidine (TMB) and urea peroxide are added. ELISA can provide a useful measurement of antigen or antibody concentration. Although most ELISA kits are qualitative assay, quantitative kits do exit.

Dry Chemical colorimetric assay

Dry Chemical Colorimetric Assay Kit, based on Enzyme Reaction Chemistry colorimetric principle, are chemical testing process, which is different from the immuno interaction between antigen and antibody.

During the test, the fixed chemical reagents will solve into the liquid specimen, which will react specifically with the target analyte of the test kit. The newly developed compound then causes a visually detectable color change in the test pad. The different concentration of the analyte in the liquid specimen causes different degree of color changes. By comparing the resulting colors with the standard color chart attached to the test kit, the concentration of the target analyte can be estimated.

This technique is widely used in medical diagnostics, and urine reagent strip is one typical application. In the urine test strips, certain quantities of different chemical reagent(s) are fixed in up to 14 pads along a plastic back lining. The color changes can also be read with urine analyzer, an instrument which actually is a reflectance photometer that analyzes areas on the urine strip and displays the results in clinically meaningful units. The other common application of chemical colorimetric assay is alcohol test strip.