For quick assessment of enzyme activity or protein and nucleic acid quantification, microplate readers have become a reliable and obvious choice for any lab. These multipurpose instruments facilitate research by minimizing operational time, improving processes and efficiency, and saving costs. Microplate readers are everywhere, in drug discovery, basic research, bioassay validation, and biopharmaceutical manufacturing, with applications ranging from simple ELISAs to high-throughput detection.
With a constantly evolving number of reagents, kits, and accessories, determining the right microplate reader for your lab is a challenge. Readers can be equipped with specific or multiple detection modes, accept a variety of plate layouts, and include additional automated functions, with base readers starting at around $4,000 and going up from there. Aligning the right features with current and future lab needs can help determine the best microplate reader for you.
What to consider
Primary considerations when choosing a microplate reader are throughput and flexibility. In labs where throughput is a top priority, a device that can screen 96- to 1536-well microplates in under one minute is worthwhile. If flexibility becomes important in a growing lab supporting a variety of projects, the decision might come down to whether a multimode reader that offers additional capabilities better suits the lab’s needs. Additionally, user experience and benefits such as ease of use and optimization functions, as well as integrated software and built-ins, might offset extra costs.
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With a goal of performing high volumes of biochemical or pharmacological tests and achieving maximum efficiency, high-throughput screening or sample testing must be fast, minimize sample use, and maintain a high level of sensitivity. Microplate readers can play an influential role in the success of an experiment, enabling more difficult to detect targets to be quickly identified in a reproducible manner. Evaluating throughput requirements can help direct plate format and device decisions, such as whether a monochromator, hybrid, or laser detector is most useful.
Another important consideration lies in the assay types to be run and the flexibility of the instrument. Will you be running simple quantitation assays or are there plans for experiments with multiple type requirements, as there are for core facilities? Assay types dictate what modes are needed. Modalities such as absorbance, fluorescence, and luminescence are the most frequently used in laboratories worldwide. Yet, depending on the application, advanced modes including fluorescence polarization or time-resolved fluorescence could be preferred. If there are multiple assay types to be run, flexibility is key. Multimode instruments provide the flexibility to run a variety of applications on the same instrument.
When taking into account user experience and additional features, make sure to focus on current needs and potential growth. Easy-to-use instruments contain more automation, such as wavelength selection, optimization, and built-in protocols with integrated software. More complex workflows and high-throughput assays might benefit from a more comprehensive workstation setup. The latest iterations of readers tend to have modular configurations, where base instruments can be customized to fit a variety of user levels and with upgradable options.
Microplate reader modalities
Microplate readers use different modes to detect light emitted by samples in a plate. Light emission is the result of a biological, chemical, biochemical, or physical reaction, which is then measured and quantified by a detector, usually a photomultiplier tube (PMT).
The type of wavelength selection system can impact what modes can be incorporated as well as what reagent technologies can be used. While filter-based detection is more sensitive and less expensive, instruments with monochromators are more convenient, easy to use, and can run spectral scans across varying wavelengths, expanding the number of assays that can be performed. Newer versions offer hybrid optical systems integrated into one instrument. While hybrids were initially believed to compromise the quality of both approaches, advances in technology have eliminated this concern.
The traditional absorbance microplate reader calculates absorbance as the ratio of light intensity illuminated on and then transmitted through a sample. The amount of absorbed light correlates to the concentration of the sample, so is ideal for nucleic acid and protein quantification or colorimetric reactions. Inclusion of a UV/vis spectrometer enables high-performance and full-spectrum absorbance measurements, instead of requiring specific wavelength selection. This allows faster data collection of typically 1 second or less per well of the entire absorbance spectrum (~200 to 1000 nm).
Fluorescence microplate readers offer sensitive and precise detection of any fluorescence intensity assay, with better dynamic range than absorbance approaches. When a fluorescent molecule emits light upon excitation by a higher energy light source, the emission is filtered, collected, and measured. With a diverse array of fluorophores, fluorescence intensity assays can include single or multiple colors in one experiment. FRET assays can also be measured, where an excited donor transfers energy to the acceptor, which will emit light without external excitation sources. Compatible applications include receptor studies, fusion assays, protease assays, or immunoassays.
Luminescence microplate readers do not need an excitation light source. Instead, light is emitted resulting from a chemical or biochemical reaction. Reactions can be flash (bright and fast) or glow (slow and dim) and can use BRET (bioluminescence resonance energy transfer) as a dual reporter detection assay. High sensitivity, low-noise photon-counting photomultiplier tubes are a popular choice for these devices, along with injectors with variable volume and automated washing functions. Luminescence detection can be used for luciferase reporter assays, cell viability, ATP measurement, and cytotoxicity assays. While wavelength selection is not required, the ability to select multiple wavelengths offers additional benefits for multiplex assays and optimizing signal to noise.
For labs that have a variety of different assays to run, multimode microplate readers might be the best bet. While multimode readers are more expensive than single-mode instruments, there has been a change in approach to lower their cost. These readers can be equipped with a modular configuration that enables selection of those detection modes to suit your current needs and the option to add others in the future as needs change. Standard multimode readers measure absorbance, fluorescence, and luminescence. Iterations of these permit add-ons of additional approaches, including time-resolved fluorescence (includes TR-FRET, HTRF®) and fluorescence polarization and can be further expanded to include AlphaScreen, BRET, dual luciferase reporter assays with injectors, and western blot detection.
Advances and options
With a constant evolution of technology, improvements, enhancements, and additional functions are changing the way we use microplate readers. Recent developments are increasing the speed and sensitivity of assays, in addition to introducing automation for easier operation and upgradable functions that incorporate more of the workflow.
Some multimode readers require manual adjustment of PMT gain voltages to optimize sample signals, which is cost-effective but takes time that can result in loss of sensitivity or signal over-saturation. Other readers have automated the dynamic range selection for easier and quicker assay setup and optimal reading range based on signal intensities, allowing both bright and dim samples to be read with equal sensitivity. Vendors are also integrating excitation lasers to significantly improve performance and lower limits of detection. Compared to xenon lamps, lasers produce higher excitation energy at a specific wavelength for high-throughput assays, TRF, or Alphascreen applications.
Taking a more comprehensive approach, workstations combine multistep workflows into one automated instrument. Microplate assays, such as ELISAs, consist of several biochemical steps including reagent dispensing, incubation, shaking, wash steps, and reading. Automated stackers, heaters, and stirrers for reagents, microplate shakers, and washers, and enhanced touchscreen workflows that simplify tasks and store protocols are making assays ever more convenient.
Look for instruments that can be upgraded with different modalities and accessories should your needs change. A barcode reader, programmable injectors, and dual-channel configurations are useful features that can increase throughput. Additional accessories help to enhance the instrument performance and improve sample processing, from atmospheric control units for live cell-based assays and flexible temperature control to data syncing on network computers and LIMS integration. No matter how simple or complex your reader requirements may be, there are myriad options for both specific needs and broader possibilities.