What are the differences between ELISA and “ELISA-like” assays?
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The acronym ELISA stands for Enzyme Linked Immunosorbant Assay. Two descriptive facets in that name are Enzyme Linked and Immunosorbant. In a standard ELISA a protein, either antibody or antigen, is coated, or absorbed, onto specially coated plates. The last step in the assay is detection. This is done by the converting of a substrate, such as ABTS, into a colored product (chromogenic detection) by an enzyme that is conjugated to the detection antibody. The one most are familiar with is Horseradish Peroxidase or HRP. The HRP enzyme converts the substrate into a colored product whose absorbance is then measured.
ELISA-like assay formats, as I refer to them, have the development and procedural roots in the standard ELISA, but are not ELISA by the strictest definitions. Even a fluorescent ELISA is not technically and ELISA since the detection signal is fluorescent and not the result of an enzyme converting a substrate. When I say procedural roots of an ELISA, I refer to the steps of an assay. MSD assays use a chemiluminescent detection but the assay steps are very similar to an ELISA. It is the serial addition of reagents/samples separated by wash steps that I refer to when I describe an assay format as ELISA-like.
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