Absorbance detection measures the ability of a sample to absorb light of a specific wavelength. It was the first detection mode available in microplate readers more than 3 decades ago. Unlike other detection modes, absorbance is a measure through the sample. Absorbance microplate readers determine the amount of light absorbed by a sample by quantifying how much of the light the sample was exposed to is transmitted through it. Hence absorbance readers require a light source illuminating the sample, an optical filter or monochromator, selecting a specific wavelength, and a light detector positioned on the opposite side measuring the amount of transmitted light. In spectrometer-based readers a selection of the wavelength is not necessary as the whole spectrum (usually from around 220 to 1000 nm) is acquired.


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Absorbance assays


Absorption of light is often referred to as the Optical Density (OD) and is a function of the concentration of a sample. Consequently, absorbance detection can be used for quantification purposes.


Common applications include ELISA assays, bacterial growth, enzyme activity assays, and DNA/RNA and protein quantification. Moreover, conventional colorimetric analyses have been adapted to the microplate format and can be quantified by plate readers.

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