Microplate readers measure the results of enzyme-linked immunosorbent assays or "ELISA" tests and other light absorption-based tests.
In the simplest of terms, a sample is treated to a sequence of chemical processes, and usually some rinses, which are designed to generate a measurable color change to indicate the presence of a chemical of interest. This color change is measured optically by a microplate reader.
Many assays generate a color change that can be read by measuring the absorbance of the result at a specific wavelength. Other assays, such as fluorescent, may generate a fluorescent signal to be measured using a different technology.
Microplates are a common container for managing higher volume ELISA samples and testing. An entire industry has been built around the design and manufacture of microplates, liquid handling devices for microplates, readers, robots, and automated microplate handling platforms.