by Catherine Shaffer
A major problem in the past with DNA and protein gels has been the difficulty in getting good images and data from them. Photographs under white or UV light have proved inadequate for quantification, and the entire process of manipulating the camera and gel, and developing the film, is imprecise to say the least. Modern gel documentation systems are designed not only for convenience, but for high accuracy and precision in telling you how much of your target molecule is in the gel, and where it is. "Gel documentation system" is actually a broad term used for many different types of imaging systems from a basic imager for protein and DNA gels, to a very versatile instrument that can be used for western blots, cell cultures, and even live animals in addition to gels. Choosing a gel documentation system, therefore, depends heavily on what the planned applications are.
Replacing the Polaroid
Many scientists learned to document their gels using a Polaroid camera. Although modern CCD imaging techniques are far superior to film for quantitation, a surprisingly large number of people held on to the Polaroid. All of that changed in 2008, when Polaroid discontinued its instant analog hardware and film products, forcing a switch to digital among the remaining instant-film diehards. The difficulty is that many CCD camera systems are simply "too much" for basic gel documentation needs. Alpha Innotech (San Leandro, CA) has introduced its Red Imager as a plug and play solution for labs that need an imager that is as quick and convenient as their old polaroid camera. Lisa Isailovic, marketing manager for Alpha Innotech, explains: "You put it on your bench top and turn it on, and it is installed. There's no assembly required. The streamlined touch screen interface is designed for labs that want image capture to be easy, and a system that doesn't require any user training."
Red is best used for gels less than fifteen centimeters square, for DNA and protein gel imaging using UV or visible light. Red does not image chemiluminescent or fluorescent westerns. Alpha's Fluorchem Q and related products are designed for more extensive imaging and documentation needs.
Imaging and More
One of the advantages of digital imaging over film is that there are so many more possibilities when you consider the permutations of different light sources and dyes, the latest optics technologies, and powerful software analysis. Alpha Innotech's Fluorchem Q, for example, surpasses film in accuracy, and has multichannel detection ability, making possible detection of several species in one experiment—a powerful option for the researcher who wants to step up from a basic imager like the Red.
With the constantly shifting landscape in science, and a tight economy putting the squeeze on funding, it's worthwhile to think about future upgradability in addition to present needs. If equipment already bought and paid for can be upgraded with an improved camera or other component, that's a major savings for the laboratory. Carestream Molecular Imaging (Rochester, NY) has gel documentation systems (Gel Logic 212) that are made with future upgrade potential in mind. The 212 is the entry level gel imaging system. It has manual controls, and a scientific grade CCD camera. This model is a more complete imaging system that is upgradable to chemiluminescent and fluorescent imaging.
The next piece of the puzzle is making the use of your system is critical. Most researchers today use digital systems at 1/3 to 1/2 of their full potential. Having controls to completely engage an imaging system’s potential is critical. Carestream is developing a suite of new features for the next Gel Logic system, including automation in gel handling and controls. According to Craig Smith, product manager for Carestream, these features will help scientists get as much data as possible from their samples. "Enabling scientists to make better use of the camera, and get better data is critically important. That's the focus of our features." Carestream is also one of the few companies to offer integrated safety features in its imagers to prevent exposure to UV light and other hazards.
Although the Gel Logic systems are designed for protein and DNA gels and gel-like experiments like western blots, they have proven marvelously versatile. A small number of Carestream customers have found fascinating applications for their gel documentation systems. Says Smith, “Gel use accounts for about 97% of samples imaged. The remaining 3% can be all over the science spectrum. Says Smith, “some (researchers) image swarms of bacterial colonies while other agricultural-based labs may need to image outer leaf structure.” Robust system controls are needed to handle a variety of samples and Carestream Molecular Imaging systems have developed some of the best. The Gel Logic platform, and future platforms, coupled to excellent integrated controls, will enable the researcher to capture better images, obtain better data, with less effort.
Resolution—Not Just for New Year's Anymore
A CCD camera-based gel documentation system is as easy to use as a basic Polaroid camera system and can deliver powerful quantitative analysis. Not all cameras are equal, however. The GelDoc-it™ Imaging System, by UVP, LLC (Upland, CA) offers the highest resolution, scientific grade CCD camera available for this category of products. Boasting a full 2-megapixel resolution for superior image quality. GelDoc-it also features the patented FirstLight® UV transilluminator, with a coefficient of variation (CV) of less than five percent (<5%) over the full imaging area.
When illuminating fluorescent gels using a standard transilluminator, the amount of light returned by the fluorophore could vary as much as 50%. Slight differences in gel placement could lead to very big differences in fluorescence detected between different gels, or the same gel on different days. This illustrates the typical CV of standard transilluminators. The patented technology in the FirstLight transilluminator design eliminates much of this variation, which makes the overall quantitative image analysis more consistent and reliable. Says Alex Waluszko, vice president for marketing and sales at UVP, "If you take the same gel, put it on a standard transilluminator inside a typical gel documentation, and slide it over two inches, the data will change, because of the non-uniformity. The use of the FirstLight prevents reliance on uniformity correction by software that can lead to low signal data loss. We're the only ones that have FirstLight with extremely uniform UV illumination."
Economics and application needs will heavily influence the choice of a gel documentation system. A laboratory that needs a basic workhorse imager for daily PCR runs may lean toward a basic, workhorse imager, whereas a lab with diverse research programs or an interdisciplinary group with shared resources might want a step-up imager with fluorescent and chemiluminescent capabilities and state-of-the-art optics. It's clear, however, that a complete gel analyzer has quite a lot to offer compared to the old film-based methods.