It can be found in any immunology laboratory in the world. Indeed, the 96-well plate is one of the simplest and most ubiquitous pieces of kit in biomedicine. It is a rectangular plastic plate containing 96 little depressions or wells neatly arranged in 8 rows, labelled “A” to “H”, and 12 columns, numbered “1” to “12”. Test reagents react within any one of 96 mini wet laboratories – identified individually from A1 to H12.
The plate is synonymous with the enzyme-linked immuno-absorbent assay (ELISA), a standard method of detecting whether a target biochemical substance is present in blood, body fluids or other biological material. The intensity of the colour change seen in a positive result can also indicate how much target material is present.
The 96-well plate and the ELISA have formed the basis of everyday biomedical tests, such as those for pregnancy, HIV and food allergens. The assay – another word for test – has become one of the standard methods of detecting the presence or absence of a target antigen, whether it is a fragment of sex hormone, bits of parasite or indeed, in the case of HIV, the protein antibodies created by the body’s immune defences in the presence of the virus.
The “microplate” first came to prominence in 1976 in a landmark scientific paper by Alister Voller and Dennis Bidwell of the Institute of Zoology in London (Manual of clinical immunology, 1976, p506-12). They were the ones who first saw the potential for using such plates as a way of quickly and efficiently using the ELISA method to test dozens of blood samples for the presence of dangerous pathogens, such as trypanosomiasis, malaria and rubella.
Such immunodiagnostic tests rely on first coating each plastic well with the target antigen, such as the protein of a virus or parasite present a person’s blood serum. After a series of steps involving washing and incubating, if the antigen in question is indeed present it forms a bond with a specific antibody attached to an enzyme – the enzyme-linked, immuno-sorbent bit of the process. This enzyme then catalyses a change in colour of another reagent, called the chromogenic substrate, and it is this colour change, often read automatically by a spectrometer, which denotes the presence of the target agent.
Three groups of scientists independently and simultaneously developed ELISA in 1971 using test tubes, about 10 years after an immunoassay using radioactivity was developed to measure insulin. But it was Voller and Bidwell who first saw the potential for using microplates for detecting human pathogens under field conditions and insisted the technology was not covered by commercial secrecy. They later wrote: “This paper showed that highly sensitive methods could be very simple and could be used both within and outside the conventional laboratory. We believe that this paper contributed towards better health care of millions of people, animals and plants throughout the world.”
The 96-well microplate became an industry standard, used in their millions globally with little thought about how they came to be so ubiquitous.