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Function of a Plate Reader

Plate readers (also called microplate readers) allow scientists in a range of labs to detect the biological and chemical events of samples. By detecting this directly in microtiter plates, labs are able to rapidly screen and quantify samples for experiments. Given these advantages, these instruments are valuable in industry (pharmaceutical and biotech) as well as academic labs.



Plate Readers and Microplate Readers are used for rapidly reading data in a variety of high-throughput production and R&D environments. BioSurplus has these instruments for sale.

Plate readers offer a wide range of use, and are commonly used in applications involving:

  • Research
  • Drug discovery
  • Bioassay Validation
  • Quality control
  • Manufacturing

What is the difference between a plate reader and spectrophotometer?

Both plate readers and spectrophotometers were created for the purpose of determining a sample’s absorbance via principles of the Labert-Beer law. The primary difference between the two is the balance between productivity and accuracy.

Plate readers can collect much greater volumes of data in the same amount of time due to measuring samples in a multi-well microplate, normally holding 48-96 samples. The spectrophotometer, on the other hand, will only measure one sample at a time due to using single cuvettes. Another difference is the function of the cuvette vs the microtiter plate. Additionally, the use of microplates in plate readers lends them to integration with robotic plate handlers, again increasing productivity.

While cuvettes will only function as sample holders, microtiter plates have a strong adsorption for antigen antibodies. By acting as a solid carrier, analyses are again carried out faster. Spectrophotometers also tend to allow greater selection of wavelengths, altogether giving a slightly more precise and accurate system, albeit slower than the plate handler. Modern advances and focus on plate readers have significantly shortened this gap in recent models.

Modes of Detection

Detection Mode
How It Works
Applications/Advantages
Absorbance- Light source, set at specific wavelength, illuminates sample.
- Detector quantifies light transmitted through sample, which is correlated to molecular concentration.
- Foundation for most calorimetric studies/assays.
Fluorescence- Illumination causes sample (with fluorescent label) to fluoresce.
- Detector quantifies fluorescence signal (separated from excitation light via filter) to correlate with concentration.
- Broader use and greater sensitivity compared to absorbance due to range of fluorescent labels.
Luminescence- No illumination source required.
- Light measured from (bio)chemical reactions in sample
- Often used for cell viability and cytotoxicity assays.
Time-Resolved Fluorescence (TRF)- Similar to fluorescence intensity, difference is the delayed timing of detection (after excitation light flashes)
- Requires specific fluorescent molecules (lanthanides)
- Uses pulsed light source (Xenon flash lamp) to excite longer lasting fluorescent markers
- Offers solution to background noise caused by excitation light
- Limited sensitivity but increased robustness
- Used in Screening applications (time resolved fluorescence energy transfer)
Fluorescence Polarization- Similar to fluorescence intensity, difference is inclusion of polarizing filters
- Samples excited with polarized light, leading to samples emitting polarized light based on mobility
- Large molecules will emit polarized light when excited
- Molecular Binding Assays (small fluorescent molecule binds to larger, non-fluorescent molecule)

Different Categories of Plate Readers

Plate readers come in two general categories: single-mode and multi-mode.

Single-Mode

Stand-alone formats are generally restricted to one primary mode of detection (as listed above). Such single-mode models include:

  • Absorbance microplate reader (Visible or UV/Vis)
  • Fluorescence microplate reader
  • Chemiluminescence microplate reader

Multi-Mode

More modern plate readers are better equipped to handle a range of tasks required by research and production labs. To do so, these plate readers are designed to carry out the entire range of detection modes. These are called ‘Multi-mode’ plate readers, and allow labs to economically gather a range of data in one instrument.