Josh P. Roberts has an M.A. in the history and philosophy of science, and he also went through the Ph.D. program in molecular, cellular, developmental biology, and genetics at the University of Minnesota, with dissertation research in ocular immunology.
Peeking into a research lab today, it would be rare to see a line-up of microplate readers on a bench, each capable of performing only a single type of measurement. If a lab requires instruments to read ELISA plates, one to do fluorescence and one for luminescence, it will likely look for one instrument that can handle all these tasks. In fact, there is a trend among multimode plate readers to incorporate other capabilities (such as imaging)—to “take traditional things that happen on a lab bench and put them all into one system,” notes Celeste Glazer, product manager for bioresearch at Molecular Devices.
At the same time, enhanced capabilities are available to complement the traditional modes; these often are provided as optional modules. Witness the availability of injectors, fluorescence-polarization filters, environmental controls and laser/filter combinations to perform amplified luminescent proximity homogeneous assay (ALPHA) experiments, using, for example, Perkin Elmer’s AlphaScreen® and AlphaLISA® assay technologies. Here we discuss the evolution of multimode microplate readers.
Togetherness
When Eric Matthews, midwest sales manager at BMG, started out 15 years ago, the performance of single-mode readers was typically better than what could be found in multimode readers. “Compromises were made” to get all the functionality into a single box. “But this is no longer the case,” says Matthews.
The savings are not only in bench space, but also in cost. “That’s because you only have one transport mechanism in there, one stacker, one incubation chamber,” points out Jason Greene, senior product marketing manager for BioTek Instruments. “So you’re only paying for the additional modes within that box.”
Multimode plate readers include, at the very least, some combination of absorbance (typically covering the UV/visible range), fluorescence and luminescence. In some cases, the configuration as purchased is the final configuration. For example, Molecular Devices’ SpectraMax M2 can read absorbance and fluorescence intensity, and its SpectraMax M3 can also read luminescence. However, “those are separate instruments,” says Glazer. “You could trade up from an M2 to an M3, but you couldn’t open it up and add anything to it.”
Yet many (especially higher-tiered) instruments are modular, in the sense that the capabilities can expand with the lab’s needs. For example Thermo Fisher Scientific’s Varioskan LUX base model comes standard with absorbance and fluorescence, “but on to that – either at the time of purchase or later on – you can add other modes such as luminescence and time-resolved fluorescence and AlphaScreen®, as well as dispenser capabilities and a gas control module,” notes technical application manager Michelle Smits.
All these options
Many readers such as Promega’s GloMax Discover focus on general absorbance, luminescence, and fluorescence based assays, as well as fluorescence resonance energy transfer (FRET) and bioluminescence resonance energy transfer (BRET) assays, says Michael Bjerke, Promega global product manager. “Our strategy is to make things really simple” by offering a complete package integrating Promega assays and robust, easy-to-use instrumentation to run them. “Users don’t have to do anything except hit a button on the machine and it’s ready to go. If [users] do have issues, which might not involve the instrument or the assay at all, a single phone call is all users need to get support for their experimental design, reagent assay and instrument.”
Other assays, such as TRF, time-resolved FRET (TR-FRET), homogeneous time-resolved fluorescence (HTRF), fluorescence polarization (FP) and ALPHA screening, are more of a niche market that the majority of users do not do.
That said, such technologies “have been pushed into the academic laboratory from the high-throughput screening environment, and a lot more labs are interested in doing that—even at a pretty low-budget research level,” notes Matthews. Thus more and more instruments, including BMG’s CLARIOstar, support such assays and even feature endorsements from reagent suppliers saying the reader is “HTRF compatible,” “LanthaScreen Certified Plus,” Transcreener Validated” or “DLR [Dual-Luciferase Reporter] Ready,” for example.
When shopping for a multimode microplate reader, researchers should anticipate and plan forward into their experimental and assays needs: “Get those technologies upfront, or consider an instrument that allows them to add them in the future,” says Smits. This should include more obvious items like a light source capable of exciting ALPHA assays or injectors necessary for fast or kinetic assays. Also important are shaking and environmental controls that keep beads or cells in suspension and assay at the correct temperature and pH. To get the best sensitivity for cell-based assays, it is better to collect measurements as close to the bottom of the plate well as possible, using bottom-detection capabilities, notes Greene.
Still Need More?
Beyond improving upon detection sensitivity and speed in various detection modes, there is a trend to add cell-based imaging to instruments’ capabilities—enabling multiple orthogonal techniques to be performed in a single well. Recent offerings from Molecular Devices, BioTek, PerkinElmer and Tecan all incorporate image-based multimode microplate readers, notes Glazer. Not to be confused with more costly high-content analyzers (HCAs), most of these are low (around 4x) magnification imagers with the entire well as the field of view—which is useful for cellular localization or cell counting, for example. “You couldn’t look at really small, subcellular localization, for example,” Glazer says.
One exception pushing the detection capabilities of the multimode reader is BioTek’s Cytation 5, which combines automated, digital widefield microscopy with conventional multimode microplate detection to provide phenotypic cellular information and well-based quantitative data. The instrument offers up to 60x magnification in fluorescence, brightfield, hematoxylin and eosin (H&E) and phase-contrast channels, explains Greene.
Plate readers can be stand-alone devices sampling one plate at a time, or they can be integrated – software and hardware – with robotic and liquid handling external systems. Some instruments can be controlled wirelessly. With instruments such as Promega’s GloMax Discover and Explorer Systems “you can push all the data to the cloud automatically from the instrument, or you can network or integrate it with a laboratory information management system (LIMS),” says Bjerke. “Or if you’re old school and like to use a USB stick, that’s fine.”
With all the capabilities available in multimode microplate readers to consider, after the researcher’s needs are met, ease of use is typically the most important purchasing consideration, Smits says. Check the specs, but then kick the tires: “Get it in your lab and test it. Really make sure you’re comfortable with the user interface, and also make sure it performs the way you need it to for your assay.”
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