Traditional ELISA typically involves
chromogenic reporters and substrates that produce some kind of observable color change to indicate the presence of antigen or analyte. Newer ELISA-like techniques use
fluorogenic,
electrochemiluminescent, and
quantitative PCR reporters to create quantifiable signals. These new reporters can have various advantages, including higher
sensitivities and
multiplexing.
[6][7] 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 nanoparticles as a chromogenic reporter was able to give a naked-eye colour signal from the detection of mere
attograms 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.
[8]
https://en.wikipedia.org/wiki/ELISA I am a sustaining contributor to The Wikimedia Foundation
I investigated ELISA and its economics during the recent cryptosporidium out breaks. Early in the Ebola EVD outbreak, Ebola reagents were US$300 per microgram from China.