ELISA swapped radioactive tags for a colour change and transformed lab testing
Before 1971, detecting a specific protein with antibodies meant using radioactive labels. Two teams, one in Stockholm and one in the Netherlands, found a safer trick: chain an enzyme to the antibody, add a chemical it acts on, and watch the well change colour. The deeper the colour, the more of the target present.
Immunoassays began with radioimmunoassay, published by Rosalyn Sussman Yalow and Solomon Berson in 1960, in which radioactivity served as the signal. Because radiation carries health risks, researchers sought a non-radioactive stand-in. Enzymes such as horseradish peroxidase produce a colour when they meet substrates like TMB, but the enzyme had to be attached to an antibody, a linking step worked out separately by Stratis Avrameas and G. B. Pierce, and the target had to be fixed to a surface so leftovers could be rinsed off, a technique that Wide and Jerker Porath described in print in 1966.
Working separately in 1971, Eva Engvall and Peter Perlmann at Stockholm University, and Anton Schuurs and Bauke van Weemen, combined these pieces into the enzyme-linked immunosorbent assay. In a simple version, the sample is stuck to a plastic plate, often with 96 wells, a blocking protein such as casein coats any bare plastic, an enzyme-tagged antibody binds the target, and a substrate reveals it. Washing between steps with mild detergent strips away anything loosely attached.
The enzyme is the secret amplifier. Even a handful of bound antibodies keep churning out coloured product, and more binding means faster colour. The weakness of the direct approach is that every protein in a serum sample can cling to the plastic, crowding out a scarce target. The sandwich format fixes this by first coating the well with a capture antibody that fishes the target out of the mixture.
Results can be a yes or no, with the cut-off often set at two or three standard deviations, or a number read from a standard curve of known concentrations by measuring how much light passes through the well. Newer relatives use fluorescent or electrochemiluminescent reporters, and a 2012 nanoparticle version gave a naked-eye blue or red answer from mere attograms of material. ELISA is used across medicine, plant pathology, biotechnology and industrial quality control.
Source: ELISA
