Which device in a plate reader functions to amplify the detected light?

The photomultiplier tube is the device in a plate reader that amplifies the detected light. This type of tube is highly sensitive and works by converting incoming photons into electrons. When light strikes the photomultiplier tube’s photoelectron surface, it releases electrons that are then accelerated by an electric field, resulting in a cascade effect. This means that a single photon can ultimately produce a significant number of electrons, thus amplifying the original signal.

This amplification is critical in laboratory settings where even very low levels of light need to be detected for accurate readings in assays and experiments. The other devices listed, such as the light guide, photodiode, and detector element, serve different roles, such as directing light or converting light into an electrical signal, but they do not provide the same level of amplification that a photomultiplier tube does.