Absorbance
Absorbance detection has been available in microplate readers for more than 3 decades, and is used for assays such as ELISA assays, protein and nucleic acid quantification or enzyme activity assays (i.e. in the MTT assay for cell viability). A light source illuminates the sample using a specific wavelength (selected by an optical filter, or a monochromator), and a light detector located on the other side of the well measures how much of the initial (100%) light is transmitted through the sample: the amount of transmitted light will typically be related to the concentration of the molecule of interest.
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