Radiolabelling, enzyme labeling, luminescent labeling, fluorescent labeling, and immunogold labeling techniques are all examples of labeled immunoassay techniques.
1. Labeled immunoassay of radioactive materials
Yalow and Berson invented the radioimmunoassay (RIA) in 1959, which is a revolutionary approach combining radionuclide tracer technology with high sensitivity and specific immunochemical technology.
The labeled immunoassay approach leverages the nuclide marker's amplification effect to raise the lower limit of detection of the material being tested, while employing antibodies or antigens as binding reagents, considerably enhancing the assay's specificity.
2. Labeled immunoassay using fluorescent labels
Conn et al. developed fluorescently labeled immunoassay (FIA) in the 1940s. The antigen or antibody is labeled with a fluorescent material that binds to the appropriate antigen or antibody, and the fluorescence intensity is measured using a fluorescent microscope or UV irradiation. The fluorescent labeled immunoassay is a technique for measuring fluorescence intensity and fluorescence using a fluorescent microscope or UV light.
Although the fluorescent labeled immunoassay approach is very sensitive, fluorescein can be physiologically hazardous, reducing the antibody or antigen's sensitivity and selectivity.
3. Labeled immunoassay technique with enzyme labeling
After immunofluorescent antibody technique and radioimmunoassay, it is a key new serological technique. In 1966, Nakane et al. and Avrameas et al. reported using enzymes instead of fluorescein-labeled antibodies to develop the enzyme-labeled antibody approach (Enzyme-labeled antibody technique) for the localization and identification of antigens in biological tissues, respectively.
Engvall Van Weemen et al. published the enzyme-labeled immunosorbent test in 1971, making enzyme-labeled antibodies quantitatively detectable for the first time.
Immunotransfer techniques based on enzyme-labeled antibodies were created in the 1980s for the detection and identification of protein molecules.
Immunoenzymatic labeling techniques are now widely employed in immunodiagnosis, detection, and molecular biology research.
4. Labeled immunoassay with luminescent labeling
Foreign nations began using chemiluminescent chemicals to mark antigens or antibodies around the end of the 1980s, resulting in the development of luminescence immunoassay technology.
Luminescence immunoassay (LIA) is a term that refers to chemiluminescence immunoassay (Chemiluminescence immunoassay, CLIA).
Besides, electrochemiluminescence immunoassays and enzyme-amplified chemiluminescence immunoassays are also available (ECLIA).
CLIA was developed by Sohrocler and Halman in the late 1970s, and it combines luminescence's high sensitivity with an immunoassay's specificity. The basic principle of the same enzyme labeling assay is the use of chemiluminescent reaction reagents (can be luminol or catalysts, etc.) labeled antigen or antibody, labeled antigen and antibody, and to be tested after a series of immune reactions, physical and chemical steps (such as centrifugal separation, washing, etc.), and finally to determine the form of luminous intensity determination.
5. Labeled immunoassay using superparamagnetic particles
The Magnetic Immunochromatofraphic Test (MICT) is a mix of current physics and biotechnology that was originally employed in the field of basic medicine to create and construct magnetic assays [13,14].
Unlike other labeling techniques, magnetic particle labeling is unaffected by colored impurities, allowing it to be used to directly quantify colored substances such as blood, food, and sewage. The premise is that superparamagnetic nanoparticles are utilized as markers, and the local magnetic field impact of the magnetic particles attached to the immune complex is monitored by a very sensitive magnetic detection apparatus to produce a quantitative result of the analyte under investigation.
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