Basic information about microplate readers
A microplate reader is a laboratory instrument that is used to measure chemical, biological or physical reactions, properties and analytes within the well of a microplate. A microplate consists of small wells in which separated reactions take place. These reactions convert the presence of an analyte or the progression of biochemical processes into optical signals. The microplate reader detects these signals and thus quantifies the parameter of interest.
Scientists in the life sciences and pharmaceutical industries strive to improve routine laboratory processes and efficiency by using products or instruments able to save time. A microplate reader can handle up to 3456 samples in minutes or even seconds. A plate reader helps to minimize operational time and to save reagent costs, allowing researchers to dedicate more time to data analysis and generation of actionable insights.
A microplate reader is used for the quantification of several biological and chemical assays in a microplate. Nowadays, the availability of a plethora of reagent kits enables the exploitation of a microplate reader in different fields and for many different applications. Besides biological, biochemical and pharmaceutical research, both in academic and industrial environments, plate readers are also used in environmental research, and in the food or cosmetics industry.
A microplate reader detects light signals produced by samples which have been pipetted into a microplate. The optical properties of these samples are the result of a biological, chemical, biochemical or physical reaction. Different analytic reactions result in different optical changes used for analysis. Absorbance, fluorescence intensity and luminescence are the most popular and most frequently used detection modes in laboratories worldwide. Additionally, advanced modes such as fluorescence polarization, time-resolved fluorescence and AlphaScreen® are also available.
Microplate-based measurements detect light signals produced by a sample, converted by a sample or transmitted through a sample. The signal is measured by a detector, usually a photomultiplier tube (PMT). PMTs convert photons into electricity that is then quantified by the microplate reader. The output of this process is numbers by which a sample is quantified.
Depending on the nature of the optical signal changes during a reaction and consequently on the detection mode, samples may need to be excited by light at specific wavelengths. This light is usually provided by a broad band xenon flash lamp. In order to allow excitation of the sample only by specific wavelengths, the light produced by the lamp is selected by a specific excitation filter or monochromator. To increase sensitivity and specificity, filters or monochromators are equally employed on the emission/detection side. These are usually placed between the sample and the detector.
How do I find the right microplate reader?
Which assays would I like to do?
When a microplate reader is to be procured, there are already applications known that are to be measured. However, it makes sense to pay more attention to this question in order to find the right and future-proof solution for the laboratory. On the one hand, you will have to run basic assays to quantify biomolecules such as nucleic acids and proteins, or cell viability. For all these applications, several solutions are available that are based on different principles, detection modes and sensitivities. Therefore, it is important to know in advance the exact name and supplier of the kit or the chemistry you want to use. On the other hand, there are thousands of tests that answer specific biological questions. There may be solutions to problems that you usually solve with cumbersome tests, although simpler solutions based on microplates are available. Therefore, reviewing your day-to-day lab work and gathering information on how colleagues use microplate readers is a fundamental step before you buy a microplate reader.
Different assays are differently detected, even though they might answer the same biological question. If you already decided on commercial kits, you will find the required detection mode in the product insert. Otherwise, detection modes that are available in a microplate reader and what they are typically used for are described below.
Absorbance measures how much light is lost (absorbed) when transmitted through a sample. Molecules often absorb light at a specific wavelength and can be quantified by measuring their absorbance. Typical applications that are read in absorbance detection mode:
|Protein quantification assays||Bradford, Lowry, ELISAs, BCA|
|Cell viability assays||MTT, WST, XTT|
|Microbial growth assay||OD600|
AlphaScreen (Amplified Luminescent Proximity Homogeneous Assay) technology uses beads that release singlet oxygen when excited with red light (680 nm). Singlet oxygen molecules move up to 200 nm and react with thioxene in a chemiluminescent reaction. Further energy transfers lead either to broad luminescence signals between 520 and 620 nm or to signals with discrete wavelengths. If donor beads (singlet oxygen releasing) and acceptor beads are in close proximity, a luminescent signal is emitted. These beads are usually brought together by antibodies that specifically bind to the same analyte, or that are coupled to molecules that interact with each other. For AlphaScreen detection, excitation at 680 nm is combined with a luminescence readout that is delayed in time, compared to the excitation. AlphaScreen is often used for high throughput applications studying the following:
|Protein, cytokine quantification||AlphaLISA assays|
|Protein phosphorylations||Alpha SureFire assays|
|Protein-protein interactions||AlphaScreen assays|
Fluorescence Intensity (incl. FRET)
Fluorescence is the absorption of light energy and its transformation into emission light, next to kinetic energy and heat. Since the emitted light is lower in energy than the input light, emission is always of higher wavelength. The process of energy uptake, energy conversion and light emission is quick and occurs in a nanosecond timeframe. Hence, the detection of fluorescence intensity occurs as follows: excitation with light at a specific wavelength and detection of the emission light at higher wavelength at about the same time. The wavelength selection is accomplished via filters or monochromators. The intensity of fluorescence is linear to the concentration of a fluorophore and is accordingly used to quantify fluorescent (or fluorescently labelled) molecules. Other fluorescence intensity applications employ a shift in fluorescence emission or an increase of fluorescence when interacting with a molecule of interest to detect a specific molecule. Typical fluorescence applications are the following:
|Cell viability assays||Resazurin assay, Calcein-AM|
|Aggregation assays||Thioflavin T (RT-QuIC)|
|Enzyme activity assays||4-methylumbelliferone (4-MU), NADH-based assays, 7-Amino-4-Methylcoumarin (AMC)|
|Reactive oxygen species||H2DCFDA assay, DCF assay|
|Nucleic acid quantification||Qubit assays, Quant-iT assays (e.g. PicoGreen)|
Another fluorescence-based detection mode uses polarized light to excite the fluorescent molecule. The change of polarization of the emitted light is determined by measuring the emission in the parallel and perpendicular plane relative to the excitation polarization plane. Changes in fluorescence polarization result from differences in molecular weights. Small and light molecules move quickly and depolarize fluorescence emission whereas bigger molecules move slowly and retain fluorescence polarization. This principle allows to study the following:
|Competitive binding assays|
|Nucleotide detection to report on enzyme activities||Transcreener assays|
Luminescence (incl. BRET)
The emission of light without prior excitation is referred to as luminescence. The production of light in life science experiments occurs in course of a chemical reaction and is either spontaneous or needs enzymatic catalysis. In a spontaneous luminescent reaction, the substrate as well as co-factors need to be present to generate light. For an enzyme-dependent luminescent reaction, a functional enzyme is essential. Such an enzyme is called luciferase. In order to detect the emitted light of a luminescent assay a detector is necessary. Typically, all light coming from a well is bundled by a lense and guided to the detector. Accordingly, luminescence detection does not rely on filters or on an excitation source. This very sensitive detection mode is used to study the following:
|Cell viability assays||CellTiterGlo|
|Reporter assays||Dual luciferase reporter assay|
Nephelometric measurements determine light scattering in a solution. To this end, light is sent into a sample and the forward scattered light is measured. This way, the concentration of particles in solution can be monitored. This helps to investigate:
|Solubility of drugs|
Time-resolved fluorescence is a method based on fluorescence. Hence, it needs excitation of the fluorescent sample at a specific wavelength and detection of the emitted fluorescence at a specific wavelength. Compared to conventional fluorescence intensity, the emission endures for a millisecond instead of a nanosecond timeframe. This is made possible by Lanthanides, rare earths with long-lifetime fluorescence characteristics. These allow to measure the emission signal with a delay to the excitation and avoids the detection of background and autofluorescence. This is employed for these applications:
|Metabolic assays||soluble probes for extracellular acidification and oxygen consumption measurements|
|Biomolecule and protein quantification||Immunoassay, DELFIA|
A detection mode which is closely related to time-resolved fluorescence combines time-resolved fluorescence with Förster resonance energy transfer (TR-FRET). The lanthanide long-lifetime fluorophore acts as donor and transfers its energy to an acceptor fluorophore. Since transfer only occurs when both fluorophores are in proximity, this method is often used for binding studies.
|Binding studies||TR-FRET-based assays|
Our single-mode readers
These microplate readers can measure one detection mode only. They are the best choice if it is known upfront that the device will be occupied by one application only. Such tasks are typically long-term assays that block the microplate reader for other measurements. Therefore, one detection mode is sufficient. Examples for such studies are microbial growth monitoring which takes one or more days, or Thioflavin T experiments which take up to 7 days. A single detection mode satisfies your laboratory, if you can perform all your tasks in a single detection. For instance, with absorbance measurements you will be able to measure enzyme activities, quantity of DNA and proteins, cell viability and many more. But you are limited to assays that might have lower sensitivity or specificity than assays employing other detection modes. If you currently plan applications based on one detection mode only, but you are not sure what the future brings, look out for instruments that can later be upgraded with further detection modes.
Our multi-mode readers
Instruments capable of reading two or more detection modes are called multi-mode readers. They offer a higher flexibility regarding the assays that are possible to read. They are recommended whenever many users work on the machine, when your applications change from project to project or, if you already know you need to read assays with different detection modes. Furthermore, a multi-mode reader is more cost-effective than buying dedicated single-mode readers for each detection mode.
6 up to 96 well plates
Up to 96 well plates, there is often a good signal that can easily be detected, and 96 wells are measured comparatively quick. They can be read by most microplate readers. High sensitivity and speed are required for these plate formats if you wish to examine quick kinetic measurements such as calcium fluxes or assays with small signal changes such as biosensors.
Image ©Greiner Bio-One GmbH
384 well plates
When working with 384 well plates, the time it takes to measure the plate as well as the sensitivity required to measure it become more important. For fluorescent readouts, the use of a focusing system is beneficial as it increases sensitivity. Instruments avoiding crosstalk are recommended for luminescence measurement in 384 well plates. As the wells of this plate are closer together, the light is more likely to shine into adjacent wells.
Image ©Greiner Bio-One GmbH
1536 and 3456 well plates
As these plate formats are very dense and can be used with low volumes (< 10 µl) only, dedicated microplate readers are needed to measure them. They require exact positioning, high speed and high sensitivity in order to record smallest signals in a reasonable time.
Image ©Greiner Bio-One GmbH
Microplate readers with highest sensitivity allow you to read very low signal intensities and to have a better resolution of signals within your assay window. This is most important if your negative and positive control are close together. In order to still identify changes in between positive and negative control, a highly sensitive instrument is needed.
Instruments providing high measurement speed are recommended to measure high density plates (1536 and 3456 well plates), if high throughput is desired (measuring hundreds of plates a day) or if a high temporal resolution is needed to resolve quick events (e.g. second messenger signaling).
If your needs change during one project or between projects, an instrument is recommended which provides numerous possibilities. The possibility to switch detection modes, to easily switch between top and bottom reading or to change wavelengths in absorbance and fluorescence-based measurement without the need to manually built-in new filters. These features are typically provided by monochromator-based multi-mode readers.
Microplate reader accessories extend the capabilities of your instrument. The add on functionalities are required for specific applications such as live cell assays, mid-throughput readings or low volume readings.
When it comes to the decision to buy a microplate reader, of course budget plays a role.
The price of a microplate reader depends on the technical equipment and the number of detection modes that the device can measure. The price range starts at 2.500 Euro for a simple filter-based ELISA microplate reader and could go up to over 100.000 Euro for a high-end and dedicated multi-mode microplate reader with a plenty of detection modes and the best technology for unmatched measurement results and highest sensitivity.
But be careful with your choice and don’t consider only your current, but also your future needs.
Keep an eye on the possibility to upgrade your microplate reader with additional features or detection modes at any time. If you have the chance to upgrade your instrument later, you don’t need to buy an additional instrument for future applications. This saves not only money and useful space in your lab, but also time that you must bring up to get used to a new instrument or brand.
Beside the costs for the microplate reader itself, there could be additional costs to be considered when selecting the right instrument for your lab. Don’t forget to check if there are any hidden costs, e.g. fees for servicing, support, software updates and licenses or any bundled reagent packages.
Also keep in mind that filter-based readers are usually cheaper than monochromator-based instruments, but you need to purchase different filters for different wavelengths. Be sure to factor in those costs as well.
BMG LABTECH is specialized in producing microplate readers only and brings 30 years of full expertise in microplate reading technology. This knowledge gets visible in the results that our instruments deliver - the only factor that counts in your lab! BMG LABTECH users can trust to receive best results in sensitivity, speed and flexibility. Moreover, our plate readers are developed to provide optimum performance for years. Our instruments are developed, produced and tested in Germany and are built to be extremely robust and reliable.
One quality seal is our product ranking on the established scientific platform "Select Science", where our customers gave us 4.7 out of 5.0 stars. Don't miss to read what our users have to say about our microplate readers.
Due to their modularity, all our plate readers can be equipped with different detection modes and cover a multitude of applications. Additional features can be upgraded at any time. This gives you the chance to keep your options open even if you don’t use the full scope of your microplate reader right at the bat.
At BMG LABTECH we strive to provide you with the very best customer service. If you need customer support, we are only a phone call or email away. During business hours, you immediately speak live to a person who is happy to assist. There is no automated phone system or waiting in a queue, our scientists, engineers and technicians are always there to help.
All our instruments come with a multi-user software package that can be installed on as many computers as users requires, without the need to purchase licenses. Software updates for our microplate readers are of no charge within the first 12 month after purchase.
Finally, we guarantee availability of spare parts for at least 10 years after a product is phased-out. That’s how long we keep components in stock for your plate reader!