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.
When it comes to microtiter plate readers, there’s no shortage of information; Biocompare last covered the topic in May. But there’s a difference between what’s available and what you need.
Biocompare spoke with the directors of some shared-facility cores to get their perspectives—and indirectly, their clients’—on microplate readers. What should someone think about when considering a purchase? What is useful, and what is not? Are there any specific capabilities that customers are asking for?
Of course there are. As with most things, there are as many opinions as there are researchers. Your needs may differ, so take it all with a grain of NaCl.
Multi-modal
The most basic and popular flavors (“modes”) of readers measure the absorbance, fluorescence or luminescence of samples in a 96-well plate. The first question a user should ask is: What types of assays will be run on the instrument? There are readers dedicated to a single detection mode, but increasingly users are turning toward “multimode” readers that can handle different tasks from the same box.
An individual lab that does the same task over and over again and always needs just one kind of reader “can buy that single-function reader because it’s always cheaper,” says Lan Chen, who runs the chemical genomics core facility at Indiana University School of Medicine. Such instruments tend be relatively user-friendly, with easy-to-navigate software.
If your lab runs assays requiring more than one detection mode, it might be better to get a multimode reader. A multimode box is usually about the same size as a single-mode reader, so you’ll save bench space vs. having two (or more) dedicated instruments. Also, most vendors’ “single-mode machines are actually their multimode machines without the bells and whistles,” says David Solow-Cordero, director of Stanford University School of Medicine’s Bioscience Screening Facility Shared Resource. “They sell one higher-end instrument, and then you just get whichever modules you want on it.”
Some vendors do offer lower-end, dedicated instruments in addition, but in general such a reader is “probably not going to be very versatile or expandable in the future,” says Brian Jespersen, manager of the Michigan State University Pharmacology and Toxicology core facility. Thus, it may need to be replaced sooner rather than later, or another instrument may be needed to fulfill the future need.
Versatility
Before purchasing a new instrument, Jespersen recommends getting the end users engaged in the selection process by identifying both current and future applications it likely will be used for. Understand how the machine is expandable, and know what additional options might be available, he says.
Say you want luminescence and absorbance capabilities now, but know you’ll need to do fluorescence down the road. If you don’t have the budget for all those modalities all at once, ask the vendor if you can buy some modules now and upgrade later, suggests Solow-Cordero. The instrument likely will be able to accommodate all currently available modules, but there’s always the chance that some specific modules won’t work in conjunction with others, so be sure to double-check.
In addition to detection modes—which run the gamut from fluorescence, luminescence and absorbance to more specialized modalities like time-resolved fluorescence, fluorescence polarization and Alpha screening—multiplate readers can be equipped or integrated with a variety of accessories. Fast instruments with plate stackers, liquid handling and barcode readers, for example, make for easier high-throughput applications like library screening. So too does the ability to accommodate 384- or even 1536-well plates, notes Chen.
The ability to read from the bottom (as well as the top) of a plate is helpful for looking at live cell cultures, while heating and cooling functions enable certain enzymatic and growth assays.
A monochrometer can be a real boon, says Solow-Cordero: “You can just type in any wavelength, type in your cutoffs, and do very specific excitation and emission that way.” Otherwise, users are “constantly changing out the filters or dichroics, and no one wants to deal with that anymore.” Filters generally are regarded as more sensitive, but monochrometer technology has improved to the point that Solow-Cordero no longer sees an advantage to using filters. Jespersen, though, says some monochromators may not be able to discriminate wavelength as well as dedicated filters, which can potentially complicate assays such as multiplex ELISAs, depending on the protocol or the labels being used.
Niche
Although many investigators believe an injector is a necessity for luminescence assays, Solow-Cordero calls that “sort of an old-school way of reading.” “People thought that when you read luminescence, you [had] to read the first 10 seconds, the burst of it,” he says. In actuality, after the burst the signal stabilizes to a level directly proportional to the amount of initial signal, “so that you can just add your reagents off-line and then read an entire plate.”
Alpha screening capabilities once were available only on instruments from PerkinElmer, but “now everyone else has built their own sort of Alpha screen-compatible laser, and that can be added on,” Solow-Cordero says. His core doesn’t offer that capability; he says there are many other technologies that are essentially the same, which his instruments can handle. “But for some reason, people get stubborn and want to do it—they read a paper that used Alpha screen, and that’s what they’re going to do.”
Jespersen’s core recently purchased a BioTek Cytation3 fluorescence reader with brightfield imaging, temperature control and shaking capabilities, which his users were asking for to do time-lapse studies. The instrument costs $40,000 to $50,000 and is upgradable to include other modalities.
Yet Solow-Cordero questions whether an imaging module on a multimode reader would be good enough to meet the needs of most of his users. “I think imaging is very useful, but you buy an imager for that. You get a dedicated machine,” which, he says, can run a quarter- to a half-million dollars.
Service
It’s important to heavily evaluate the terms of a service contract before signing on; many “are a waste of time and money,” Jespersen says. He urges users to understand the business model that the company is operating under—whether it is trying to make money from the instrument sale or the service contract.
It’s also important to know how long a company will provide service for an instrument, and whether service will even be available to customers who opt out of a contract, says Solow-Cordero.
Yet sometimes it’s the intangibles that sway a decision. Investigate different instruments. Try to see them in a colleague’s lab or ask the vendors for a demonstration, especially if you have a specific niche application in mind.
And finally, consider the user experience by “play[ing] around with the software” that provides the interface between the user and the hardware, says Eric Chow, director of the Center for Advanced Technology core facility at the University of California, San Francisco.
Do all that, and you can be confident your reader will serve you now and into the future. And that’s an opinion you can count on.
Image: BPAE cells at 20x magnification captured by a BioTek Cytation3.