A microplate reader with a 96-well microplate in the sample drawer. Plate readers, also known as microplate readers or microplate photometers, are instruments which are used to detect biological, chemical or physical events of samples in microtiter plates.hile plate reader usually refers to the devices described above, many variations are available. Some examples of other devices working with the microplate format are: 1  ELISPOT plate readers, used to count the colored spots that are formed in the course of ELISPOT assays.