The history of microplate readers— now on the market for more than 30 years—explains the ongoing increase in applying this technology. Plate readers are used in many applications, including bioassay development, diagnostics, drug discovery, food testing, and quality control. The expanding range of applications parallels the large number of detection modes, including absorbance, AlphaScreen, fluorescence polarization, time-resolved fluorescence (TRF), time-resolved fluorescence energy transfer (TR-FRET), luminescence, and spectrophotometry. In a survey by Lab Manager, 90 percent of the respondents used absorbance detection and roughly three quarters also used AlphaScreen and fluorescence polarization.
As Gary Barush, global director of marketing and sales at BioTek Instruments (Winooski, VT), says, “Microplate readers continue to be used extensively in absorbance mode in lots of diagnostic testing.” He also points out an ongoing migration of the technology from human to animal and food testing. He adds, “We’re seeing a significant movement into cell-based assays.” In a recent BioTek survey, 96 percent of respondents indicated an interest in using or developing cell-based assays. Nonetheless, he adds that “about half of the market will still use biochemical assays.”
In addition, Kasia Proctor, product manager for the microplate reader line at Molecular Devices (Sunnyvale, CA), says, “Over the last couple of years, there’s been a trend in adopting new technologies such as the AlphaScreen assay capabilities.” She agrees that more scientists want to run cell-based assays, and that’s why her company developed its new SpectraMax, which includes an imaging cytometer option that can be used, for example, in quality control before running a cell-based assay.
The movement to cell-based assays requires changes in various aspects of the technology. For one thing, vendors must make the appropriate reagents available. In addition, changes in microplate readers come in handy. As an example, Peter Banks, PhD, scientific director at BioTek, says, “Bottom readers are very good for live-cell assays.”
Technical aspects of detection
Microplate readers can collect information with various technologies. “At first, most microplate readers used filters for wavelength selection,” says E.J. Dell, PhD, international marketing director at BMG LABTECH (Ortenberg, Germany). “Then monochromators became available in plate readers.” Now plate readers combine technologies, using filter sets with either a spectrometer or a monochromator.
By using a monochromator or spectrometer, a researcher can use most any wavelength for detection. Filters have higher sensitivity, but the detection range is constrained. To get the best of both worlds, says Dell, “a flexible monochromator-based instrument with the sensitivity of filters is needed.”
|Based on our most recent survey, the primary applications readers are using their microplate readers for in their labs include:|
|Authenticity and traceability||1%|
|Biomolecule concentration measurement||13%|
|High-throughput drug screening||3%|
|In vitro fertilization (IVF)||1%|
|PCR setup and cleanup||2%|
|Stem cell research||3%|
An increasing number of plate readers offer multimode detection. “Once you make the capital investment in multimode detection,” says Barush, “it covers you for more assays.” In such flexible platforms, though, Banks warns customers to find “flexibility without compromise.”
Many scientists want to use microplate readers in phenotypic screens. For example, a drug-discovery experiment could assess the cellular response to a compound. In this situation, a reader should include imaging capabilities. “These phenotypic assays can look at morphological change, so imaging can be really powerful,” says Banks.
The combination of microplate reading and imaging can speed up screening. Imagine that some feature of a disease can be tracked with the fluorescence mode of a microplate reader. Next, a drug could be applied and the microplate reader’s fluorescence detection could find wells that responded to the treatment. Then, imaging can be used to further analyze only the wells that showed the fluorescence change.
The move to cell-based assays demands other new features on plate readers. For example, some readers include atmospheric control, such as regulating oxygen and carbon-dioxide levels. Some also provide temperature control. “Readers can also include shaking to mix the cells,” says Dell. “In addition, most instruments read in the center of a well, but cells are unevenly distributed. So our instruments can read 900 points per well, thereby giving a digital image.”
Advances in the software make up another key trend in today’s plate reader technology. As Banks says, “One of our customers beta testing our new Cytation3— which can be used as a multimode plate reader and for imaging—uncrated the instrument, got it running, and started collecting images in about twenty minutes.”
Proctor adds, “The key is with the software, because that’s how you interact with a reader.” The software can also add new capabilities to a reader. For instance, Proctor says, “we’ve added functionality to our software, providing lots of data analysis and graphing options so you don’t need to export that data.”
The right microplate reader depends on the user and the applications. “Most microplate readers can do many of the assays out there,” says Dell, “but the technology inside the readers differentiates how well they can do them.”
Thomas Maynard, PhD, director of the George Washington Institute for Neuroscience at the George Washington University (Washington, DC), studies the development of the nervous system and how it is impacted by genetic disorders. He says that one of his lab’s key uses of plate readers is “to measure growth factors in the developing embryo. In a recent paper in Human Molecular Genetics, we measured the activity of retinoic acid and sonic hedgehog in the developing brain of embryos carrying a genetic mutation.” When asked about any improvements that he’d like to see in microplate readers, he mentions that the software on some microplate readers “is a bit challenging when training new people,” but he calls that his “only minor complaint.”
Customers should be sure to know what options exist for excitation, such as different lamps or lasers. Other options might include the capability of running kinetics assays, which require injectors to add a compound while quickly taking measurements.
Today’s variety of microplate readers demands careful shopping to make the best choice.
For additional resources on microplate readers, including useful articles and a list of manufacturers, visit www.labmanager.com/microplate-tech