It’s been a year since Biocompare last provided an overview of Western blot documentation systems, and though the marketplace is crowded, it is by no means stagnant.
New systems have been launched for both chemiluminescent and fluorescent Western blot documentation. Many use touch-screen interfaces for reduced benchtop footprints, and some feature modular designs for easy upgrades in the field. Most vendors report an emphasis on ease of use in their onboard image-acquisition software and a focus on improved reproducibility and quantitation.
Here’s what you need to know when considering a new Western blot documentation system or upgrading an existing one.
Key considerations
Though colorimetric and radioisotopic detection are still widely used, most Westerns these days utilize either chemiluminescence or fluorescence detection. The former, by all accounts, is the most widely used option, and likely the more sensitive. Ning Liu, a product manager in the life science group at Bio-Rad Laboratories, reports sensitivity gains of “six- to 10-fold” compared to fluorescence. Fluorescence produces a more stable signal but also higher background. Yet it also enables multiplexing (that is, the detection of two or more proteins simultaneously). “The experimenter needs to be cautious about cross-talks among the fluorescent channels and cross-reactivities resulting from mixing antibodies,” Liu says.
Researchers are divided as to which detection method is better for quantification. Many believe fluorescence provides more reliable numbers, as fluorescent signals are relatively constant over time while chemiluminescence, being the result of an enzymatic reaction, rises and falls. Others are less convinced, such as Lisa Isailovic, marketing director at Azure Biosystems. “The variation from chemiluminescent blot to chemiluminescent blot is probably no greater than from fluorescent blot to fluorescent blot,” Isailovic says. (The SuperSignal™ West Dura reagent from Thermo Fisher Scientific and Clarity™ ECL from Bio-Rad Laboratories both promise relatively constant light output for at least several hours.)
If you plan to use Western blotting for quantification purposes, pay particular attention to its ability to handle situations in which weak and strong signal bands are present on the same blot. Ideally, the system software will have sufficient dynamic range to capture the weak band without saturating the strong signal, such that the measured difference between the two accurately reflects the protein quantities in each.
As a general rule, Western blot documentation systems are multifunctional. In addition to chemiluminescent and/or fluorescent blots, these often can image DNA and protein gels, microtiter plates and colorimetric Westerns. The Odyssey CLx, from LI-COR Biosciences, can even be used for small-animal whole-body imaging, says senior product marketing manager Jeff Harford (though he recommends the dedicated Pearl Trilogy imaging system for that application, if it is being done at large scale). Thus, in selecting an imaging system, identify first what your lab’s particular needs are.
The Omega Lum™ C and Omega Lum G from Gel Company, for instance, are both capable of capturing chemiluminescent blots. But the Omega Lum C is optimized for chemiluminescence work, and the Omega Lum G is intended for labs working mostly with DNA and RNA gels and the occasional Western, says Margaret Sharp, sales and marketing manager. With a faster, more sensitive camera and “wide-open aperture,” the Omega Lum C “can collect very faint signals very quickly, so it’s about four times faster at taking images than the G”—a time savings that may pay dividends in a more Western-focused lab.
When making a purchase, be sure to consider the user experience. How easy is image acquisition? And how much lab real estate will the instrument consume? Though some imagers are controlled by external PCs, many new systems feature touch-screen computer interfaces for simplified instrument control and image acquisition as well as a smaller benchtop footprint. Oftentimes, these systems are able to determine the best settings for image acquisition with little to no user input. “The software determines the optimal exposure time, so you are utilizing the full range of the imager,” says Liu of the software powering Bio-Rad’s latest ChemiDoc instrument, the ChemiDoc Touch. “It eliminates the need to do repetitive hit-or-miss guesswork to find the best exposure, as people routinely do with film.”
Finally, consider your future plans. Many manufacturers have embraced modular designs, enabling researchers to buy an introductory system and add features as their requirements change.
Selected instrumentation roundup
Azure Biosystems launched its c-series imagers (the c150, c200, c300, c400, c500 and c600) about 1.5 years ago, according to Isailovic. The systems are easy to use and have a small footprint, she says, “but we stand out with flexibility.” The fully configured c600, which the company calls its “Ultimate Western System,” includes blue light, white light, UV transillumination, chemiluminescence, and visible and near-infrared fluorescence. The lower-end c200 (the “Gel Documentation Workstation”) supports only blue- and white-light imaging, as well as UV. But users can add any of the c600’s features via a simple field upgrade, Isailovic says, meaning it’s possible to convert a c200 into a c600 as the need arises. “We call that ‘future-proofing,” she says. (The c150 is not upgradable.)
Bio-Rad Laboratories launched its new ChemiDoc Touch Imaging System in October 2014. According to Liu, the system is specifically targeted to researchers who still use film for chemiluminescent imaging—a group that includes some 50% to 60% of the Western blotting market, he says. “The main focus of that system was [providing] the highest-level sensitivity and resolution, so they could get a film-like result.”
According to Liu, though film is generally less sensitive and has a poorer dynamic range than digital systems, it traditionally has been preferred in some situations, especially when capturing very weak signals, because the film is placed directly on top of the blot. “That’s where digital imagers over the years have not been able to deliver.”
Powered by an iPad-like touch-screen interface, the ChemiDoc Touch features an overhauled optical system relative to its sibling ChemiDoc instruments, Liu says, including a faster lens, updated camera and shorter working distance between the blot and the lens. The result is a system that outperforms film for the most sensitive applications, he says.
The Gel Company expanded its Omega Lum line with the Omega Lum W in April 2015. Capable of measuring both chemiluminescence and three-channel multiplexed fluorescence imaging, the Omega Lum W features a simple touch-screen interface, says Sharp. “You put your blot on the tray, put the tray inside the system, select your application from the app list in the software and press ‘capture.’ The system does everything automatically.” (Omega Lum C users can upgrade their systems to the W in the field, Sharp says.)
Another recent release from Gel Company is Imagel, a combination of iPhone/Android app and phone adaptor for imaging DNA and protein gels using a smartphone camera. “It’s not a scientific-grade camera, it’s not cooled, it doesn’t do chemiluminescence,” Sharp says. “But it’s a very cool tool for gel documentation.”
GE Healthcare Life Sciences launched its Amersham WB System in September 2014. Comprising two pieces of hardware, the system enables users to reproducibly run and image a gel, blot it, probe and wash the blot and then image the results with a laser-based scanner. User intervention is required at key steps, says Kim Cushing, product marketing manager, “so it’s not automated, but it is integrated.” The Amersham WB System uses pre-cast gels and dedicated reagents to drive two-color (Cy3/Cy5) fluorescence Westerns, Cushing notes, with one channel reserved for total protein detection and the second for the targeted protein. It is particularly helpful in ensuring consistency from experiment to experiment. “The blotting process is somewhat lacking in reproducibility generally,” she says. “Having everything integrated in one system and dedicated reagents gives you confidence in your results.”
LI-COR Biosciences offers three systems for Western blot documentation: the chemiluminescence-only C-DiGit, the chemiluminescence/fluorescence-capable Odyssey Fc and the near-infrared fluorescence-only Odyssey CLx. “Odyssey CLx is probably our most popular system,” Harford says.
According to Harford, LI-COR’s systems excel in image quantification, featuring a sufficiently wide dynamic range that “you cannot saturate or blow out an image in most circumstances. You never have to take a second exposure.” That, he explains, reduces experiment time and increases reproducibility, “especially on the chemiluminescent side of things.”
Syngene’s portfolio includes the chemiluminescence-only GeneGnome XRQ and the “more versatile” G:BOX and PXi lines, according to Guy Fiddian, internal sales coordinator at Synoptics Ltd, Syngene’s parent company. Both G:BOX and PXi include UV and blue LED transillumination and visible-light fluorescence-imaging capabilities, but they differ in viewing area and optical details. The modular, upgradable G:BOX line includes the popular G:BOX Chemi XRQ, with a 4-megapixel (MP) camera and fixed stage, and three instruments with movable stages: the G:BOX Chemi XT4 (4 MP), G:BOX Chemi XX6 (6 MP) and G:BOX Chemi XX9 (9 MP).
The PXi features a smaller footprint than the G:BOX series, and the PXi Touch includes a built-in touch-screen computer. The newest member of the product line is the PXi Access. Launched in March 2015, the PXi Access features a larger viewing area than the original PXi instruments (up to 21x17 cm, compared with 13x10 cm).
These new systems are vying with literally dozens of others in an exceptionally busy product arena. For those setting up new labs or simply looking to upgrade existing hardware, the choices may seem daunting—but don’t be overwhelmed. Explore the features and options and make a decision based on your research needs today as well as down the road. You will be capturing exciting new Western blot results with any of these systems.