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Product literature for Invitrogen's E-gels®, a precast agarose gel system, neatly summarizes the purported advantages of such products: "E-gels make agarose electrophoresis as easy as Plug & Play." The vast majority of researchers are perfectly capable of pouring their own gels, of course--the process is certainly not difficult. It may, however, be tedious. It can also be tricky; leaks are a constant bugaboo, and gel-to-gel variation can be a problem. And some of the reagents are downright nasty--unpolymerized acrylamide, for instance, is a neurotoxin. Companies such as Carlsbad, Calif.-based Invitrogen and Milford, Conn.-based Jule hope that these considerations will prompt you to think twice before pouring your own electrophoresis gels.
Since the first precast gels were introduced nearly two decades ago, many life science researchers have been foregoing messy agarose, toxic acrylamide, and malodorous TEMED (tetramethylethylenediamine) in favor of disposable gelatinous slabs, prepackaged in neat little cassettes just waiting to be loaded. Designed to fit into standardized gel rigs, these cassettes offer tremendous advantages over lab-poured gels--namely time, convenience, safety, and reproducibility--but at a price.
Of course, not everyone avails themselves of such conveniences. Typical among academics is Dominique Broccoli, associate member at Fox Chase Cancer Center in Philadelphia, who feels it is "absolutely valuable" for her students to know how to pour their own gels. Cost, too, she says, prevents her lab from going the precast route, although she would consider buying a precast gradient gel for a special project.
Courtesy of Gradipore
While Broccoli doesn't know anyone "who admits to using precast gels," clearly many academicians do--of the 4.25 million gels sold last year in the United States, says Chris Higson, a product manager for Australian gel supplier Gradipore, more than one-third were purchased by university researchers.
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Since The Scientist last examined this field,1 several manufacturers have merged, been bought out, gone out of business, or left the gel business altogether, while others have entered the market. You won't find FMC products anymore, for example; rather, the PAGEr, Reliant, and Latitude gels will all become Cambrex products as of March 31. The NOVEX brand is now part of Invitrogen's portfolio, while OWL, Hitachi, and Zaxis gels, and others have disappeared. Look instead for lines from newcomers like Montreal, Quebec-based Mirador DNA Design. Myriad options exist--agarose, acrylamide, zymogen, and isoelectric focusing (IEF) gels--but if you cannot find a product that fits your unique criteria, note that some manufacturers will custom-manufacture to your specifications as few as 10 gels.
WHAT PERCENT? Precast gels are available with agarose concentrations of 0.8% to 4%, with some companies, such as East Rutherford, NJ-based Cambrex, offering a choice of gel matrices. The gels are sometimes shipped with UV-transparent backing to prevent breakage, or--as with Invitrogen's E-Gel products--they arrive in cassettes. Most of these are compatible with a wide variety of rigs, although some, such as the E-Gels, are designed to be used only with the manufacturer's own system. Elchrom Scientific of Cham, Switzerland makes alternative submarine gel matrices, including Spreadex®, Clearose® BG, and Poly(NAT)®.
Precast acrylamide gels can be purchased with either uniform concentrations or gradients. Gels with uniform concentration range from 4% to 20% depending upon the chemistry; graduated concentrations start at 3% and extend as high as 40%. Acryl-amide gels are shipped between solid plates, generally either glass or plastic, with a few offering a choice. Hercules, Calif.-based Bio-Rad Laboratories uses a combination of supports for its Ready Gels.
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Some companies offer acrylamide derivatives or synthetic acrylamide-like polymers in similar configurations, such as high-tensile strength Duracryl from Genomic Solutions of Ann Arbor, Mich. Stacking gels are usually available, such as in products from Akron, Ohio-based Biotech Holdings Gelux.
SUPER-SIZE THAT Precast gels are made in a variety of sizes, with a variety of well configurations. Cambrex's Latitude agarose gels, for instance, are available in 10 (infinity) 15 cm, 24 (infinity) 14 cm, and 24 (infinity) 20 cm formats, and "fit most common chambers," according to company literature.
Acrylamide gels, too, come in a multitude of sizes. But because they must form leak-proof seals with the electrophoresis apparatus, these gels are manufactured to more exacting specifications than their submarine agarose cousins; users can refer to a company's literature to determine compatibility with existing hardware. Minigels of about 10 (infinity) 10 cm, such as RITE-gels from Solon, Ohio-based Amresco, are, according to the company's literature, "compatible with most current vertical electrophoresis tanks." Other manufacturers offer various sizes, such as Cambrex's 9 (infinity) 10 cm PAGEr, that can accommodate different rigs. Piscataway, NJ-based Amersham Biosciences offers larger gels in two sizes, the 24.5 (infinity) 11 cm and 25 (infinity) 11 cm versions of its Excel Gel. Gel thickness varies by manufacturer, and some, including Jule, offer several options.
Courtesy of G. Leka & J. Kroon, Jule Inc.
Both gel types come in several well configurations. Cambrex Latitude agarose gels, for instance, can be purchased with one row of 20 wells, or four rows of 25. Users can obtain Criterion™ acrylamide gels from Bio-Rad, with one large well--for large preparatory samples or an immobilized pH gradient (IPG) strip for IEF--or with 26-15 µl wells. Some products, like PAGEr gels, come with a comb; others, such as those from ISC BioExpress of Kaysville, Utah, do not.
IT'S ABOUT CHEMISTRY All the buffers that labs traditionally use for electrophoresis are found in precast gels. San Diego-based Embi Tec, for example, offers agarose gels formulated with TAE (Tris-acetate-EDTA), TBE (Tris-borate-EDTA), and MOPS (3-[N-morpholino] propanesulfonic acid)--the latter for RNA gels. You can even find "bufferless" technologies (as in the E-Gel system) that use ion-exchange matrices as a substitute. Gels can be ordered with or without nucleic acid-binding stains, ranging from traditional ethidium bromide to newer dyes such as Cambrex's GelStar.
Acrylamide gels, too, are available with a variety of buffers. The traditional Laemmli (Tris-glycine-SDS) formulation for protein separation, and TAE and TBE for DNA separation, are the most common. But Tris-Tricene, Bis-Tris, Tris-HEPES, and other formulations are also available, as are proprietary mixes. Most can be purchased with or without SDS and urea, giving the researcher the option of running a native or denaturing gel. Alternatively, users can purchase semi-dry gels and rehydrate them in their preferred buffers.
CLAIMS AND COUNTERCLAIMS Most researchers can pour their own gels, and the reagents are not generally expensive. Precast gels, then, are products of convenience, and their marketing reflects this fact; ads tout reliability, reproducibility, ease of use, and time savings. Still, manufacturers do extol the virtues of their products over homegrown gels.
Some companies, such as ISC BioExpress, claim to give "superior resolution," while others, such as Gradipore, boast that there is neither comb nor tape to remove, and the gels are easy to open. Gradipore claims also that its MicroGels will produce results four times faster than its nearest competitor. Jule and several other manufacturers mark their sample wells to ease loading, while Mirador's SoftGels each have unique identification numbers, allowing users to process multiple gels simultaneously.
Plastic is more hardy than glass, but glass gives superior clarity and heat diffusion. Those with novel matrices often point out that their products are less likely to rip or tear. Some trade on name recognition and reputation, whereas others promote shelf life. If you're interested in a complete system, one that is easy to use and expandable but incompatible with other manufacturer's products, consider Invitrogen's E-Gels. And of course there's price and shelf life to consider as well.
Courtesy of Amersham Biosciences
THE BOTTOM LINE Shelf life is a big bonus for some users, especially those likely to buy in bulk. ISC BioExpress' Express Gels- Endurance are formulated with a neutral (pH 7) buffer that, the company claims, "prevents the hydrolysis of polyacryl-amide to acrylic acid and results in an 18-month shelf life." Most other precast gel manufacturers guarantee a shelf life of from one month to a year. Whether that shelf needs to be at 4°C or at room temperature varies from product to product.
Cost varies depending on several factors: the type of lab (academic, commercial, government, or diagnostic); quantity; product features; and so on. As a benchmark, Cambrex's least expensive agarose gels (Reliant 6 (infinity) 9.5 cm, with or without ethidium bromide) retail for $98 (US) for a box of 20; Embi Tec's gels are priced almost identically. A box of 10 Tris-glycine polyacryl-amide gels (Invitrogen's NOVEX), the least expensive acrylamide formulation, retails for $99.50. The equivalent product from Jule retails for $95.
A ROSY FUTURE? Many manufacturers have abandoned the precast gel arena. Peter Pingerelli, the director of product marketing for nucleic acid analysis products at La Jolla, Calif.-based Stratagene--which offers CastAway® acrylamide gels, but only until the end of the second quarter 2003--blames a stagnating market. Newer technologies, including capillary electrophoresis, microfluidic "labs-on-a-chip," and automated sequencing devices, are supplanting the gel for DNA analysis, he says. A spokesman for a small acrylamide gel manufacturer--who asked not to be identified--shared these conclusions.
Several manufacturers note that the market is simply more difficult for companies with smaller sales forces and customer bases. Far from shrinking, however, the market for both precast agarose and acrylamide gels is actually expanding, says Wendy Reinemann, Cambrex's segment manager for nucleic acids.
Bio-Rad's Bill Gette concurs, noting that the market is being driven by, among other things, the boom in proteomics. Marketing reports from PhorTech of San Carlos, Calif., bear this out. US life scientists spent more than $100 million annually on electrophoresis products, according to a 2001 report on electrophoretic equipment and reagents. More recently, in a Global Laboratory Product Usage study, the company found that "the category of chemicals and biologicals showing the most growth [is] prepared electrophoresis gels."
Josh P. Roberts (email@example.com) is a freelance writer in Minneapolis, Minn.