Cell-based assays require cozy new features
Beyond the number of wells, biologists also use many plates. To analyze the contents, scientists use microplate readers, and they are advancing just as rapidly as the plates—probably even more so.
The most sophisticated microplate readers help scientists take care of their samples while they analyze them. In addition, advanced devices provide more analytical capabilities.
When asked about the most interesting new features in microplate readers, Xavier Amouretti, manager, product marketing at BioTek Instruments (Winooski, VT) says, “Cell-based assays drive most of them.” He adds, “More and more, people in research labs are working with live cells in microplates.” In many cases, a life scientist selects the live approach because it replicates biology in more realistic conditions.
To maintain healthy conditions for live cells, some microplate readers now control the sample environment for carbon dioxide and oxygen. Live cells often need other pampering, such as shaking them in just the right way. So scientists can select a microplate reader that provides a range of shaking options. As an example, Amouretti says, “Yeast tend to grow when in suspension, so you need a reader that shakes continuously while you make the measurement.”
In addition, the surge in cell-based assays spawned other advances in microplate readers. For instance, some vendors now make a microplate reader that includes a microscope. “So you can make a measurement in a well and image the cells,” says Amouretti.
In Salvatore Pizzo’s laboratory at Duke University in Durham, North Carolina, for example, lab research analyst Maggie Kennedy uses the BioTek Cytation 3 plate reader, mainly for cell-based assays. She says, “I look for versatility in a plate reader, something that can perform multiple functions in one machine.” She also appreciates that this microplate reader allows more than one mode of detection. She says, “I love the microscope function. Being able to visualize individual cells in addition to getting a general fluorescent signal of a well will be very beneficial to our research.”
Dialing in sensitivity
Despite the advances available in microplate readers, not every user runs complicated experiments. “Many of the assays that have been run in microplate readers are still used, like simple concentration measurements or looking at characteristics of a specific molecule,” Amouretti explains.
Some users, though, need more options. As an example, Ronald L. Earp, president of BMG LABTECH (Cary, NC), describes using a linear variable filter (LVF) monochromator. “It offers essentially an infinitely adjustable filter,” he says. “You can set the center wavelength and set the bandpass. Traditional monochromators have only one, or few, specific bandpasses.” In Earp’s instrument, he says, “You can increase or decrease the bandpass of the LVF monochromator with a click and drag of a mouse.”
This capability proves incredibly valuable when working with fluorescent proteins with various emission characteristics. “There are multitudes of them,” Earp says. “You’d need more than thirty filters to measure them all.” An LVF monochromator can just be adjusted for different fluorescent or luminescent labels. It’s also possible to incorporate an LVF dichroic that enhances a microplate reader’s sensitivity. “This combination,” says Earp, “helps when you have a weak emitter or fluorescent proteins with a small Stokes shift.”
Beyond adjusting emission and detection of fluorescence, some users will want a microplate reader that provides as many options as possible. For example, a microplate reader in a core lab might be applied to a range of experiments. In such a situation, a reader that works in various ways could be the best choice. For example, some microplate readers work in fluorescence and luminescence modes, plus absorbance in some models. As Earp points out, moving from one mode to the other can be easy. “In ours,” he says, “you just click a button in the software. Then, it’s all handled automatically.” A core lab might also seek that level of ease of use to accommodate users of various levels of experience.
Shrinking the size
For people looking at DNA, RNA, or protein quantification, says Michael Fejtl, market manager of detection at Tecan Austria in Groedig, “they like small volumes, like two-microliter volumes.” He adds, “There are several low-volume plates available from different vendors.” Sometimes, though, the measurement spots require the reader to calibrate the path length—the distance to the sensor—for every spot, and that can slow down the acquisition rate. To address that challenge, Tecan developed the low-volume NanoQuant plate with 16 spots, and each one, he says, “is exactly the same path length from the sensor and does not need to be calibrated.” As a result, Fejtl says, “This is great for customers using low volume and for fluorescence labeling.”
Getting smaller cell numbers in microplate readers can also require higher sensitivity, or being able to pick up smaller signals. “Cells can clump in the wells or grow nonhomogenously, but you need to be able to read them,” Fejtl says. “Some of our new readers increase sensitivity by a factor of twenty with the optimal read function.” He adds, “That’s a key feature for cell-based assays.”
As well volumes decrease and cell-based assays diversify, the features of microplate readers keep increasing. As Fejtl says, “There’s a whole range of readers.” With a little shopping, you can find just the one for you. But make sure to evaluate all the features now available, because they keep changing, offering new ways to automate and enhance the process of analyzing microplates.
For additional resources on Microplate readers, including useful articles and a list of manufacturers, visit www.labmanager.com/microplate-tech
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