Making the Right Choice: The Next Generation of Microplate Readers

Microplate readers can be a technology often taken for granted in a life sciences wet lab. Commonplace and heavily used, these instruments are essential for research, drug discovery, bioassays, quality control, and manufacturing processes, across both industry and academia. They measure a variety of different chemical, biological, and/or physical signals and reactions from several different sample types, all within the small wells of a microplate. The chances are that most life scientists have, at one point or another, loaded a 96-well plate with their final assay reagent, and felt a knowing sense of relief upon seeing expected gradient-related color changes along the assay standards column.

The remit of microplate readers is currently expanding across a variety of different industries beyond the world of ELISAs, Bradfords, and Lowrys. A number of companies are offering high-quality systems with a range of new features and innovations. Whether selecting the right microplate reader for a new high-throughput assay, or upgrading to one with imaging capabilities for a shared academic core facility, how do you select the best one for your needs?

Tailor purchases to lab-specific needs and assays

“Readers are now being used across the food industry, material sciences including electronics manufacturing, environmental research, and increasingly for the investigation of high-throughput 3D models,” says Peter J. Brescia, Jr., Applications Scientist at BioTek, part of Agilent. “It’s important to consider both current and future needs, given the wide range of assay technologies and reader configurations available, while also considering your lab’s budgetary constraints.”

There are a lot of applications out there: absorbance, fluorescence, and luminescence as well as widefield and confocal imaging in microplates. “New technologies are always being introduced with a variety of plate reading and imaging modes, either as an entirely new instrument or as an updated module,” Brescia adds. “Instruments range from simple absorbance readers to those with the ability to perform energy transfer assays, such as fluorescence resonance energy transfer (FRET) and bioluminescence resonance energy transfer (BRET), which use more complex light paths.”

Eric Matthews, Vice President of U.S. Sales and Business Development at BMG Labtech, explains that “Use of time-resolved fluorescence or polarization to measure molecular size is often used in drug discovery. Using AlphaScreen to determine if two proteins are co-located or associated is also popular.”

Industry scientist Zachary A. Gurard-Levin, CSO of SAMDI Tech, sheds light on how his company has integrated microplate readers into its workflow. The company is known for its SAMDI proprietary technique, which combines unique surface chemistry with MALDI-TOF mass spectrometry. This is a reader-free technique, detecting molecules based upon their exact mass. Gurard-Levin’s team screens millions of compounds every few months, with microplate readers being a very useful platform for their workflows. “Conventional plate readers offer the ability to do orthogonal assays, which can provide added confidence to our data. They can measure readouts with high sensitivity and can be useful for reactions that aren’t amenable to mass spectrometry readouts—for example when studying protein-protein interactions, or for assays with very large analytes that can’t be ionized very well.”

Useful features to look out for

“The type of assay being performed is key as poor reader selection could affect results considerably,” advises Brescia. “Some assays need a very specific light path or light source requirements to perform exceptionally well, for example with amplified luminescent proximity homogeneous assays (AlphaScreen).”

The multitude of advances in plate readers can make purchasing decisions daunting, although there are particular features to look out for. “Absorbance and luminescence are a kind of core function for most microplate readers, while advanced detection methods can vary,” says Matthews. “If you're based in an academic lab and use shared equipment, it might be important to have a variety of functions available. Sensitivity is a critical factor. Monochromator-based microplate readers will be more sensitive and allow users to select a specific wavelength. In a shared academic lab, however, it might be important to have a variety of wavelengths available, although this can negatively impact overall performance. Filters are another approach and can be more sensitive, although they require you to manually select, buy, and change them.” This can be ideal for a high-throughput facility in drug discovery and development, where plates need to be read quickly, accurately, and with precision. Matthews describes a newer innovation at BMG that appears to have addressed the monochromator vs. filters issue: “Our linear variable filter-based monochromator, found in some of our models, uses filter principles to separate wavelengths, providing the performance of filters while giving scientists flexibility.”

“There are a couple of new features showing up in microplate readers that are quite interesting,” advises Cristopher Cowan, Associate Director, Instrumentation R&D at Promega, “and Promega offers a wide range of chemistries that are used with multi-mode microplate readers. For longer-term kinetic assays, there are several microplate readers integrating the capability to maintain environmental conditions appropriate to their cultured cell assays. Cellular imaging is also being added to many readers as an application. This function allows researchers to monitor the appearance of their cells or localization of cellular components during extended assays.”

GloMax® Discover by Promega is a microplate reader with luminescence, fluorescence, BRET/FRET and UV-Visible absorbance detection capabilities.

Detection systems have also advanced, according to Brescia. “Recent developments in LED-based light sources have resulted in increased sensitivity for many assay systems. Light sources such as xenon flash lamps can be used, and increased speed and sensitivity can be achieved when a laser light source is employed. Coupled with newer, more sensitive detection devices, such as sCMOS cameras with lower background noise, scientists can achieve improved assay sensitivity and better image quality across a range of assays, with some systems offering both confocal imaging in tandem with widefield imaging.”

Meanwhile, Cowan discusses the importance of considering plate well densities and the angle from which microplates are read inside the reader: “You should definitely check the range of plate well densities supported by your candidate readers. Some will only support one well density (e.g. 96-well) while others have flexibility to support a range of well densities (like 6–384-well). It’s also important to consider which side of the plate you wish to read from. Top-reading microplate readers provide better detection performance and are more common than combined top-reading and bottom-reading microplate readers.”

Gurard-Levin describes his lab’s microplate reader selection: “In our labs, specific and refined optics are important, as well as the ability to use high density plates including those with 384- or 1536-wells. We also prefer that fluorescence signals in one well don’t bleed into the other, as this means less background and more precise data. Automated injection is critical for real-time kinetics to observe reactions happening in real-time. Our microplate reader (from BMG) gives us a whole other level of data and complexity and allows us to start asking different questions, with precision, speed, and agility, with a quality that is essential to making important go-no-go decisions in drug discovery.”

Getting the most from your new microplate reader

Once you’ve chosen and purchased your selected microplate reader, Cowan suggests that for best results, scientists use the type of plate that best matches the assay they are running. For example, luminescence assays generally provide best results when run in a white plate while fluorescence assays provide best results when run in a black plate.

Brescia also shares some advice: “Even when using the best microplate reader on the market, assay development is still key—optimizing the assay and reader so that they perform to a standard needed to extract meaningful, statistically significant data. Often this can be achieved by simply running the appropriate controls and ensuring sample concentrations fall within an assay window sufficient for the sensitivity needed for the system under investigation. It is also critical to optimize multiple assay variables where they are used, such as multiplexed assays, or with assays that have both plate reading and imaging steps. Sample prep is vital. With imaging-specific assays, significant assay development can be required to ensure the generation of high-quality quantitative data.”

Choosing the right microplate reader can be a challenge. And once you have, it remains essential to prepare and optimize samples and assays carefully, using the right controls and standards, to get the most out of your reader and obtain reproducible and reliable results.

Questions to consider: What is your budget?

• Which types of assays are users running today, and which functions are necessary to support them?
• What types of assays do users expect to use in future?
• Which types of detection are required, now and in future?
• What is the minimum detection performance required? This can include overall sensitivity, dynamic range, and cross-talk performance.
• What range of plate well densities will be required?
• Are imaging and/or environmental controls required?
• Are automation and/or robotics required? This can include features such as automated liquid handling, incubation, and higher throughput instruments such as plate stackers.
• How experienced are users?
• Which types of service and support will be required, at the time of purchase and throughout the lifetime of the instrument?