Microplate readers are widely used in research, drug discovery, bioassay validation, QC and manufacturing processes for the detection of biological, chemical or physical processes in samples contained in microtiter plates. There are a wide variety of microplate readers on the market, offering different capabilities and functionalities. A number of criteria need to be considered before purchasing a microplate reader in order to ensure that the instrument chosen is appropriate for its intended purpose.
When purchasing a microplate reader, the first consideration should be whether the reader will be needed to perform only one type of assay, or whether it will be required for multiple assays. If only one type of assay needs to be performed, a single-mode detection instrument should be purchased. However, if performing a variety of different assays is required, a multi-mode instrument should be purchased.
The purchaser should consider the type of assay that the microplate reader will be expected to perform, and whether luminescence, absorbance or fluorescence detection is most appropriate
Microplate readers with integrated computer and software capability allow the user to record and analyze data in situ. However, the range of applications and analyses available may be a little more limited than the options available on an external PC.
Microplate readers that do not have integrated computer and software capabilities must be connected to an external PC for analysis of the data. While this may not be as convenient as an integrated system, it may ultimately create more options for the analysis and manipulation of data.
Absorbance is the oldest type of detection used in microplate readers. In an absorbance microplate reader, the percentage of light of a certain wavelength transmitted through the sample is recorded. Absorbance detection is commonly used for assays such as ELISA, protein and nucleic acid quantification or enzyme activity assays.
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Fluorescence Intensity Detection
In a fluorescence microplate reader, an excitation system illuminates the sample using a specific wavelength, causing the sample to fluoresce. An emission system collects the emitted light, separates it from the excitation light, and measures the signal using a photomultiplier tube. Fluorescence intensity detection has a broader range of applications than absorbance detection and generally has a greater sensitivity. However, the instrumentation is generally more expensive.
Luminescence microplate readers detect light emitted by samples as a result of a chemical or biochemical reaction. The optical system consists of a light reading chamber and photomultiplier detector that measures the light emitted by the samples during the reaction. Luminescence detection is commonly used for luciferase-based gene expression assays, as well as cell viability and cytotoxicity assays based on the luminescent detection of ATP.
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The purchaser should consider whether the microplate reader is required for a small number of predefined assays, or a comprehensive system is required that will be able to conduct most, or all, of the commonly used assays.
For simplicity of operation and for cost containment, basic multiple-mode microplate readers tend not to incorporate a shaking capability or temperature control. Some microplate readers are equipped with shaking and incubation functions, allowing users to mix the well content and easily measure samples at elevated temperatures. The temperature control also allows temperature-sensitive reactions to be carried out entirely within the reader. The shaking function can usually be programmed according to exact requirements, ensuring high uniformity throughout the sample.
A standard 96-well microplate (8 by 12 matrix) is generally sufficient for most assays conducted in academic research laboratories or clinical diagnostics laboratories. Higher density microplates (384- or 1,536-well microplates) are typically used for screening applications, when throughput and assay cost per sample are critical.
Mid-Level Microplate Readers
Mid-level microplate readers generally combine two or three of the most common detection modes in one unit (luminescence and/or fluorescence and/or absorbance detection).
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Multi-Label Microplate Readers
Top-of-the-range microplate readers combine multiple modes, including liquid scintillation counting, luminescence, fluorescence intensity, time-resolved fluorescence, fluorescence polarization and absorbance. These microplate readers allow the user to perform almost any standard assay.
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