immunoassays

The Immunoassays, also known as the Enzyme Immunoassay (EI), is a widely used diagnostic tool for detecting antigen/antibody in a patient’s blood sample. It is a highly sensitive immunological assay used to identify and quantify substances such as peptides, proteins, and hormones.

An Immunoassays involves immobilizing a target molecule on polystyrene microplates and then combining it with an enzyme-labelled antibody. The activity of the enzyme is measured by incubating it with substrate to generate a quantifiable coloured product, which is then measured using Immunoassays reader

The Immunoassays was the first screening test widely used for HIV because of its high sensitivity.
Following are some applications of Immunoassays (Alhajj and Farhana, 2022):

1. Detection of autoantibodies (anti-dsDNA, anti-dsg1, ANA, etc.) and antibodies against infectious disease (antibacterial, antiviral, antifungal).
2. Detection of tumour markers (Prostate-specific antigen (PSA), Carcinoembryonic Antigen (CEA))
3. Detection of Hormone Levels (Luteinizing hormone, Follicular stimulating hormone, Prolactin, Testosterone, hCG).
4. Screening the donated Blood for Possible Viral Contaminants (anti-HIV-1/2, anti-HCV, HBsAg)
5. Detecting drug abuse (Amphetamine, Methamphetamine, 3,4-methylenedioxymethamphetamine, Cocaine, Benzoylecgonine)

Chemiluminescence Immunoassay (CLIA)

The principle of CLIA is same as Immunoassays, except that CLIA substrates can generate light emission in the presence of an enzyme, providing a more sensitive process compared to Immunoassays. Substrates such as isoluminol or acridinium ester produce the luminescence signal in the presence of hydrogen peroxide and enzyme (“Chemiluminescence Immunoassay – an overview | ScienceDirect Topics,” n.d.).

Measurement of light produced by chemiluminescence during certain chemical reactions provides a convenient and highly sensitive alternative to absorbance measurements in Immunoassays assays. In versions of the Immunoassays using chemiluminescence, a luxogenic (light-generating) substrate takes the place of the chromogenic substrate in conventional Immunoassays reactions. For example, oxidation of the compound luminol by H2O2 and the enzyme horseradish peroxidase (HRP) produces light.

The advantage of chemiluminescence assays over chromogenic ones is enhanced sensitivity. In general, the detection limit can be increased at least ten-fold by switching from a chromogenic to a luxogenic substrate, and with the addition of enhancing agents, more than 200-fold. In fact, under ideal conditions, as little as 5 _ 10_18 moles (5 attomoles) of target antigen have been detected (“Immunology__Janis_Kuby_5th Edition.pdf,” n.d.).

Electro-chemiluminescence Immunoassay (ECLIA)

Electro-chemiluminescence Immunoassay (ECLIA) is another form of CLIA, which employs electrical current to oxidise the substrate. In comparison to Immunoassays, CLIA and ECLIA procedures have a better sensitivity and take less time for result analysis (“Chemiluminescence Immunoassay – an overview | ScienceDirect Topics,” n.d.).

References:

1. Alhajj, M., Farhana, A., 2022. Enzyme Linked Immunosorbent Assay, StatPearls [Internet]. StatPearls Publishing.
2. Chemiluminescence Immunoassay – an overview | ScienceDirect Topics [WWW Document], n.d. https://www.sciencedirect.com/topics/nursing-and-health-professions/chemiluminescence-immu noassay (accessed 3.3.22).
3. Immunology__Janis_Kuby_5th Edition.pdf, n.d.

Immunoassays

Chemiluminescence Immunoassay (CLIA)

Electro-chemiluminescence Immunoassay (ECLIA)

References:

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