Microplate readers are established workhorses of the biology lab. Starting from humble beginnings in the 1970s as a photometer designed for microtiter plates, microplate readers are now made in a wide range of formats, from single-mode reads to highly specific assays, and can accommodate multi-modes and high-throughput applications. The modern microplate reader has three main modes of detection, absorbance, luminescence, and fluorescence. Most applications are built on these detection methods combined with specific chemistries to create biochemical assays that test for research-relevant parameters.
Protein concentration can be quantified using absorbance measurements. The most common assays are the A280, Bradford, BCA, and Lowry assays. Nucleic acids can be determined using the 260/280 nm absorbance ratio. DNA and RNA can also be detected using commercially available fluorescence assays. The high number of samples per run and the lower sample usage of the microplate format has made the microplate reader a preferred method over traditional cuvette-based methods for quantification in high throughput applications, such as in drug screening.
Enzyme-linked immunoabsorbent assays (ELISAs) is one of the most popular applications of the microplate reader. An ELISA is used to measure the specific amount of an antigen, antibody, or other proteins. It is typically performed with colorimetric detection, but can be performed as well with luminescence, chemiluminescence, and fluorescence as well. As ELISAs are well characterized, easy to perform, and have many commercially available and bespoke variants, this technique is prevalent in most life science laboratories.
Reporter gene assays are a type of gene expressions assay that studies the regulatory ability of a DNA sequence. Reporter genes can be transfected via a plasmid to a sequence of interest, typically a promoter or a transcriptional element. The reporter gene can be activated by the gene when a promoter event occurs, resulting in quantifiable luminescence. Reporter gene assays are typically performed using a luciferase assay, a common and accurate method of luminescence.
Enzyme assays give important information towards enzyme activity, including identification, quantification, and insight into the rate of reaction. Kinetic enzyme assays can be performed on microplate readers in a continuous monitoring mode, if available. Changes in the concentration of substrate and product will cause shift in measurements.
Cell-based assays are a range of assays that assess the parameters of cellular populations. Common assays include cell viability, cytotoxicity, apoptosis assays, and give great insight into how cells work when presented with biological, chemical or physical stimulus. As such, it is used in typical drug discovery screening workflows, and also used in biomedical research. Microplate readers of all modes have applications in cell-based assays. Some popular assays include luminescent ATP-based assays for determining cell viability and cytotoxicity, and the MTT assay for cell proliferation in cancer research applications.
Cell-based assays are a range of assays that assess the parameters of cellular Pharmaceutical companies and core labs engaged in drug discovery will use high throughput screening the conduct millions of biochemical or pharmacological tests. Top end microplate readers are able to read plates up to 3456 wells while using very low sample volumes. This allows researchers to look at molecular interactions at scale, with the goal to find the best candidate for further development and characterization. When combined with cell imaging, high-content imaging, flow cytometry, and automated liquid handling, a laboratory can engage in a very high level of characterization of cellular environments in an automated fashion called high content screening.
Industrial applications for microplate readers can be found in the pharmaceutical and medical device, chemical, and food & beverage industries. Popular tests include endotoxin assays and mycoplasma monitoring.
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