The Criterion™ gel system and tank blotter is a mid-size, flexible polyacrylamide gel electrophoresis (PAGE) and blotting system for SDS and native 1-D and 2-D gels. It can also be used for peptide analysis, isoelectric focusing (IEF), protease analysis by zymogram PAGE and denaturing or nondenaturing nucleic acid separation. Single percentage and gradient gels of 1.0 cm thickness are available. A variety of combs provide flexibility in sample loading; 1, 12, 18, and 26 well combs are available. Empty gel-cassettes with the same combs are also available for preparation of homemade gels. Either one or two gels can be run on the system. Less running-buffer is needed due to the specially designed upper and lower buffer chambers, which are leak-free. The wells for sample loading are labeled for easy visibility; samples can also be loaded using a sample-loading guide. Samples can be loaded with a multi-channel pipette, if desired.
The Criterion™ blotter for protein transfer is available with wire or plate electrodes for transfer of either 2 Criterion™ gels or 4 Mini gels in the 2 cassette holders. To avoid overheating during the transfer, a sealed ice element is included for placing into the tank. A cooling coil is also available for the system. A blot assembly tray for presoaking filters and pads in transfer-buffer and a roller to remove air bubbles from the sandwich are also provided.
Since I used the Criterion™ system for separating membrane proteins, which separate better when SDS is included in the gel, I bought the empty cassettes with combs to pour my own discontinous SDS polyacrylamide gels. With these cassettes, I sometimes experienced that the combs were not really tight, so that a film of polymerized acrylamide covered the walls of the wells, making it impossible to load the maximum volume or pipette the protein solutions evenly into the well. I liked the width of the gels, which allowed me to run all my sample fractions from a gradient at the same time on one gel, making it easier and more reliable to compare the distribution of proteins in the gradient. The samples separated evenly over the width of the gel. I ran my gels at a lower voltage (100 V) than Bio-Rad suggested (200 V) due to the higher viscosity of the gradient media; separation was fast (approx. 2 h). Faster runs resulted in a smile effect and uneven separation of proteins.
The cassettes are opened by pressing down the opening wedge on top of the lid. Sometimes when the weld-joint of cassettes were not completely broken, I used a sturdy spatula to crack open the cassette on both sides. I was careful to not apply too much force which could destroy the gel, especially when it might be attached to both sides of the cassette. In most cases, the gel was attached to the backside of the cassette so that it was easy to remove by simply flipping the cassette with gel attached upside down onto the soaked filter paper.
I assembled the blot sandwich under buffer to avoid air bubbles getting trapped in the sandwich. For this purpose, I used a tall Tupperware container instead of the provided assembly cassette because I’d had difficulties pouring the buffer from the double chamber into the tank (after sandwich assembly) without spilling. The sandwich containing fiber pads, filter paper and the gel is placed in the cassette holders, which hold the blot sandwich tightly together without pressure; the cassette holder is then mounted into the grove of the transfer tank. A more even transfer is achieved with the plate electrodes than with wire electrodes (which I used with the Protean® III system). Since a lot of transfer buffer containing organic solvent (20% methanol) is needed to fill the tank (1.3 L), a lot of organic waste is produced. The ice element in the tank reduces the volume slightly.
The Criterion™ gel system is a very versatile and easy to use system for the even separation of many samples at the same time. Transfer is especially efficient using the plate electrode equipped blotter. There is a lot of information about the blotter and the gel electrophoresis system, including the selection of gels and their applications, available on Bio-Rad’s website. The manuals contain pictured instructions on how to use both systems, recipes for solutions, general information about all possible procedures and a short troubleshooting table. In addition, Bio-Rad’s technical service was very helpful in solving my problems with the cassettes.