by Jeffrey M. Perkel
Quick: what are the most frequently used pieces of equipment in your lab? Pipettes probably take the top spot, but gel documentation systems likely place in the top three.
A gel documentation system is really nothing more than a miniature darkroom and associated camera. In the late '80s and early '90s, these systems were literally portable darkrooms, comprising a basic Polaroid print camera mounted atop a pyramidal base. The assembly was placed over a gel on a light box, and a picture was then taken. Once the required few seconds needed to develop the print had elapsed, the resulting grayscale photo was taped into a lab notebook.
But DNA and protein gels are not merely images to be admired, like the photos in a family album; they are data. They have to be studied, analyzed, annotated, and (hopefully) published. They also have to be stored and available for later retrieval. Unfortunately, none of those tasks is simple with print images, which can be damaged or lost, and which must be scanned into a computer for subsequent image analysis.
Fortunately, today's lab workers have more sophisticated options. Modern gel documentation systems run the gamut from semi to fully automated, with multifunctional enclosures, computer-controlled excitation and detection systems, and analysis software. These apparatuses can handle not only DNA and protein gels, but also chemiluminescent Western blots, fluorescence, and even autoradiography. For the purposes of this article, we will limit our discussion to the most basic of systems—those that can handle DNA and protein gels.
Applications
When buying a gel-documentation system, begin by asking, what are my needs? Will you be using this system exclusively for DNA and protein gels, or do you also need to document fluorescence experiments, chemiluminescent Western blots, and autoradiographs? In the former case, almost any system will do, and your choice will depend on how much you want to spend and what features you decide you need; in the latter case, you will need to consider higher-end options.
"Typically the cutting-off point is, are they doing chemiluminescent Westerns?" says Peter Chiang, product manager at Cell Biosciences. Chemiluminescence requires cooled CCD cameras, which are considerably more expensive than the cameras typically bundled with gel-documentation systems.
Price
Once potential customers have determined their applications, says Chiang, the first thing they want to know is, what will the system cost me? "That's usually where the discussion starts, what is the price range," Chiang says.
Certainly, that was the "biggest factor" for Kate Hayes-Ozello, a research scientist in the College of Veterinary Medicine at Ohio State University, who was involved in the purchase of the College's two AlphaImager systems (originally sold by AlphaInnotech, and now by Cell Biosciences). "Price was the first thing I looked at," she says.
Generally speaking, a basic gel documentation system can be had for less than $10,000, and possibly less than $5,000, depending on such features as the quality of the camera, level of automation, and quality of the software bundled with the system. Cell Biosciences' gel documentation systems, for instance, run from $3,800 for a basic AlphaImager Mini, to $12,000 for a top-of-the-line AlphaImager HP.
Lighting
DNA and protein gels have relatively simple lighting requirements. For DNA gels stained with ethidium bromide or SYBR green, you'll need a UV transilluminator. For Coomassie-stained protein gels, you'll want white light transillumination. You may also want to have white light epi-illumination (that is, illumination from above) for imaging, say, bacterial plates, and/or a blue light "converter screen" that can convert UV light to blue light for excising SYBR green-stained DNA bands without damaging them. (If you do anticipate needing to excise bands from your gels, look for a system where the transilluminator can be removed from the system cabinet for easy access to the gel.)
Camera/Optics
Key to a gel-documentation system's operation, of course, are the camera and lenses used to capture the images.
"What you probably want to look at first and foremost is the camera," says Chiang, "that's usually the most expensive and most differentiating component."
Look first, Chiang says, at resolution; most gel-doc systems have "scientific-grade" cameras with resolutions between 0.3 and 2 megapixels (MP), he says—anything less than 1 MP is considered "low-end."
Next, consider the lenses. Are they fixed, or can they be zoomed? What is the maximum magnification, and is that zoom optical (that is, is the lens actually moving) or electronic (like a cell phone camera)? Is the lens computer-controlled or manual? Finally, depending on your needs, you may also want to consider how many different filters you can place in front of your camera.
The AlphaImager Mini, for instance, includes a 1.3-MP, 12-bit camera (a 12-bit camera can capture 212, or 4,096, shades of gray), a one-position filter wheel (the standard configuration includes an orange filter for ethidium bromide, though others are available), and a manual zoom lens (8-48 mm, f/1.2). The Syngene GENi includes a 2-MP, 12-bit camera, a motor-driven, six-position filter wheel, and a motorized zoom.
Ease of use
Given the amount of use you can expect a gel documentation system to see, ease-of-use is a key consideration.
"Labs should be thinking about how easy it is for me [e.g., the lab manager] to use, and how many people I will have to train," says Ryan Short, imaging marketing manager at Bio-Rad Laboratories. "Or, is the system so intuitive you can just walk up and use it immediately?"
Simplicity factored into Hayes-Ozello's purchasing decision, as the systems she was buying were to be departmental resources. "With minimal training, a user can take a picture and go their merry way," she says. "It doesn't require significant training by a core manager…. That was really what we were looking for."
Ease-of-use is difficult to quantify, Short admits, yet there are some factors to consider. For instance, how much manipulation of camera settings is required to take a picture, and how automated are those tasks? "Can you walk up to the system and push a few buttons and get a good picture, or do you have to adjust the focus, zoom, and iris?" he asks.
Software
Of course, part of the ease-of-use calculation is the software used to capture and analyze the image. Even the most basic of gel doc systems includes acquisition software, which should allow users to control brightness, zoom, and focus. But not all systems enable you to analyze the images, as well (for instance, to identify lanes, quantify the amount of DNA in a particular band, and measure its molecular weight).
The AlphaImager Mini, for instance, includes acquisition software, but analysis software is optional. The AlphaImager HP, though, includes both standard. On the other hand, Syngene includes its GeneTools analysis package with all of its gel documentation systems, says Maggie Pochyla, product and sales support specialist. "One of our core competencies is in the software," she says.
When considering the software that comes with the system, think also about the logistics of how that system will be used. Acquisition software need only be installed on the computer associated with the device, but what about analysis software? Most researchers would probably prefer to crunch the numbers on their own computer, especially if the gel doc system is in a core facility or there's a queue to use it. "You don't want to stand by the machine to do the analysis," says Short.
So, ask how many software licenses come bundled with the system, and how many upgrades you receive (or for how long you are eligible to get them). If the analysis software is networked, make sure to check with your IT department to avoid any installation hiccups.
Odds and ends
There isn't much to a basic gel documentation system, but the devil, as they say, is in the details. With that in mind, here are a few other options to consider:
Is the system upgradable?
For instance, if you don't need chemiluminescence or fluorescence now but anticipate needing those capabilities in the next few years, can you upgrade your existing system, or will you have to purchase an entirely new system? "Everyone is going for this modular type of software and hardware," says Pochyla, "so you don't have to buy the Rolls Royce, you can buy what you need."
What is the system footprint?
Space is at a premium in most labs, so the smaller the system, the better. Some gel doc systems are controlled by an associated PC; others (such as the Syngene GENi and Cell Biosciences Red) have built-in computers with touch-screen interfaces.
How will you retrieve your data? (Over a network? With a USB key?)
How easy is it to convert an image into a publication-quality figure? Can the software export to a high-res image (typically, 300 dpi or better) automatically, or will you have to use additional software (such as Adobe Photoshop) to do that?
How often does the vendor update their software?
Gel-documentation systems have a lifespan of about seven to eight years, Short estimates, and it's important to think ahead. "You want to make sure the system provides access to your current OS," he says.