Editing ELISA (section)

==History==

Before the development of the ELISA, the only option for conducting an immunoassay was [[radioimmunoassay]], a technique using [[radioactive]]ly labeled antigens or antibodies. In radioimmunoassay, the radioactivity provides the signal, which indicates whether a specific antigen or antibody is present in the sample. Radioimmunoassay was first described in a scientific paper by [[Rosalyn Sussman Yalow]] and [[Solomon Berson]] published in 1960.<ref>{{cite journal |last1=Yalow |first1=Rosalyn S. |last2=Berson |first2=Solomon A. |title=Immunoassay of endogenous plasma insulin in man |journal=The Journal of Clinical Investigation |volume=39 |issue= 7|pages=1157–75 |year=1960 |pmid=13846364 |pmc=441860 |doi=10.1172/JCI104130 }}</ref>

As radioactivity poses a potential health threat, a safer alternative was sought. A suitable alternative to radioimmunoassay would substitute a nonradioactive signal in place of the radioactive signal. When enzymes (such as [[horseradish peroxidase]]) react with appropriate substrates (such as [[ABTS]] or [[3,3’,5,5’-tetramethylbenzidine|TMB]]), a change in color occurs, which is used as a signal. However, the signal has to be associated with the presence of an antibody or antigen, which is why the enzyme has to be linked to an appropriate antibody. This linking process was independently developed by Stratis Avrameas and G. B. Pierce.<ref>{{cite journal |last1=Lequin |first1=R. M. |title=Enzyme Immunoassay (EIA)/Enzyme-Linked Immunosorbent Assay (ELISA) |journal=Clinical Chemistry |volume=51 |issue=12 |pages=2415–8 |year=2005 |pmid=16179424 |doi=10.1373/clinchem.2005.051532 |doi-access=free }}</ref> Since it is necessary to remove any unbound antibody or antigen by washing, the antibody or antigen has to be fixed to the surface of the container; i.e., the immunosorbent must be prepared. A technique to accomplish this was published by Wide and [[Jerker Porath]] in 1966.<ref>{{cite journal |last1=Wide |first1=Leif |last2=Porath |first2=Jerker |title=Radioimmunoassay of proteins with the use of Sephadex-coupled antibodies |journal=Biochimica et Biophysica Acta (BBA) - General Subjects |volume=130 |issue=1 |year=1966 |pages=257–60 |doi=10.1016/0304-4165(66)90032-8 }}</ref>

In 1971, Peter Perlmann and Eva Engvall at Stockholm University in Sweden, and Anton Schuurs and Bauke van Weemen in the Netherlands independently published papers that synthesized this knowledge into methods to perform EIA/ELISA.<ref>{{cite journal |last1=Engvall |first1=Eva |last2=Perlmann |first2=Peter |title=Enzyme-linked immunosorbent assay (ELISA) quantitative assay of immunoglobulin G |journal=Immunochemistry |volume=8 |issue=9 |pages=871–4 |year=1971 |pmid=5135623 |doi=10.1016/0019-2791(71)90454-X }}</ref><ref>{{cite journal |last1=Van Weemen |first1=B.K. |last2=Schuurs |first2=A.H.W.M. |title=Immunoassay using antigen—enzyme conjugates |journal=FEBS Letters |volume=15 |issue=3 |pages=232–236 |year=1971 |pmid=11945853 |doi=10.1016/0014-5793(71)80319-8 |s2cid=37147723 |doi-access=free |bibcode=1971FEBSL..15..232V }}</ref>

Traditional ELISA typically involves [[chromogenic]] reporters and substrates that produce some observable color change to indicate the presence of antigen or analyte. Newer ELISA-like techniques use [[fluorogenic]], [[Electrochemiluminescence|electrochemiluminescent]], and [[quantitative PCR]] reporters to create quantifiable signals. These new reporters can have various advantages, including higher [[Sensitivity and specificity|sensitivities]] and [[Multiplex (assay)|multiplexing]].<ref name="PMID18772478">{{cite journal |last1=Leng |first1=S. X. |last2=McElhaney |first2=J. E. |last3=Walston |first3=J. D. |last4=Xie |first4=D. |last5=Fedarko |first5=N. S. |last6=Kuchel |first6=G. A. |title=ELISA and Multiplex Technologies for Cytokine Measurement in Inflammation and Aging Research |journal=The Journals of Gerontology Series A: Biological Sciences and Medical Sciences |volume=63 |issue=8 |pages=879–84 |year=2008 |pmid=18772478 |pmc=2562869 |doi=10.1093/gerona/63.8.879 }}</ref><ref>{{cite web |title=Cytokine Quantification in Drug Development: A comparison of sensitive immunoassay platforms |url=http://www.bionity.com/en/whitepapers/100005/cytokine-quantification-in-drug-development.html |first1=Michael |last1=Adler |first2=Sven |last2=Schulz |first3=Mark |last3=Spengler |year=2009 |publisher=Chimera Biotech |access-date=2015-08-20 |archive-date=2015-12-22 |archive-url=https://web.archive.org/web/20151222171128/http://www.bionity.com/en/whitepapers/100005/cytokine-quantification-in-drug-development.html |url-status=dead }}</ref> In technical terms, newer assays of this type are not strictly ELISAs, as they are not "enzyme-linked", but are instead linked to some nonenzymatic reporter. However, given that the general principles in these assays are largely similar, they are often grouped in the same category as ELISAs.

In 2012, an ultrasensitive, enzyme-based ELISA test using [[nanoparticle]]s as a chromogenic reporter was able to give a naked-eye colour signal, from the detection of mere [[attogram]]s of analyte. A blue color appears for positive results and red color for negative. Note that this detection only can confirm the presence or the absence of analyte, not the actual concentration.<ref name="delaRica2012">{{cite journal |last1=de la Rica |first1=Roberto |last2=Stevens |first2=Molly M. |title=Plasmonic ELISA for the ultrasensitive detection of disease biomarkers with the naked eye |journal=Nature Nanotechnology |volume=7 |issue=12 |pages=821–4 |year=2012 |pmid=23103935 |doi=10.1038/nnano.2012.186 |bibcode=2012NatNa...7..821D |hdl=10044/1/21938 |hdl-access=free }}</ref>