Which part of a plate reader serves as the light-sensing element?

The light-sensing element in a plate reader is typically a photodiode. Photodiodes are semiconductor devices that convert light into an electrical current. They are commonly used in various optical applications due to their high sensitivity, fast response times, and ability to detect a broad range of light wavelengths.

In the context of a plate reader, when the light emitted from a sample passes through the detection system, the photodiode captures this light and generates a corresponding electrical signal. This signal is then processed to quantitatively analyze the sample, providing important data for experiments, such as enzyme-linked immunosorbent assays (ELISAs) or other assay types.

Other components mentioned, such as a photomultiplier tube, are also light-sensing devices but are generally used in more specialized or high-sensitivity applications due to their ability to amplify very low levels of light. Light guides help direct light to the photodiode but do not sense light themselves. The term "detector element" could refer to various types of detection technologies, but in many modern plate readers, the photodiode is a standard choice due to its efficiency and effectiveness in this application.