Qiagen’s MinElute Gel extraction Kit is very similar to their QIAquick Gel Extraction kit, however, it uses a slightly different column that allows you to elute the DNA in a much smaller volume (10 ul versus 30 ul) for more concentrated DNA. The DNA that is eluted has good purity and works well for cloning and other molecular biology techniques. The kit comes with everything you need (except ethanol and isopropanol) to gel extract your DNA in less than 20 minutes, most of which is the time required to dissolve the piece of gel. We are extremely satisfied with this product as it’s an easy and efficient way to gel extract DNA fragments.
The protocol is pretty standard for a column based gel purification kit and is almost identical to the QIAquick protocol. The piece of gel containing the DNA is dissolved in buffer QG for approximately 10 minutes (sometimes longer) at 50ºC. Buffer QG (yellow solution) includes a pH indicator to ensure the solution is at the optimal pH for DNA binding. At the correct pH, the solution stays yellow, however, if the solution turns purple, the pH is too high and small volumes of 3M sodium acetate pH 5.0 (not provided) should be added. Once the gel fragment has completely dissolved, isopropanol is added to the sample and it is transferred to the provided spin column (if the volume is greater than 800 ul, it must be transferred to the column in steps). To complete the protocol, you can use either a microcentrifuge or a vacuum manifold. Typically, we just use a microcentrifuge. The sample is then spun through the column, washed twice (once with buffer QG and once with buffer PE, an ethanol solution), spun again to make sure all residue buffer has been removed and finally the DNA is eluted in either water or buffer EB (included: 10 mM Tris pH 8.5). Typically, I elute the DNA in water and allow the column to sit for 10 minutes before the sample is centrifuged. Once the initial gel fragment has been completely dissolved, the rest of the protocol takes less than 10 minutes.
The manual says these columns have a maximum binding capacity of 5 ug and an 80% recovery of DNA fragments. Although I have never tried to purify 5 ug of DNA from a gel fragment using this kit, we do see an 80% recovery (whenever checked). The real advantage of this kit is that it allows you to elute the DNA in a smaller volume so it is more concentrated. This is extremely convenient if you want to use the DNA for cloning or other molecular biology techniques. The spin column protocol is fast and efficient and easier than Qiagen’s QIAEX II system (also allows you to purify the DNA in a smaller volume) that uses silica-gel particles in suspension.
The MinElute Gel Extraction Kit does have one major disadvantage: The kit is not recommended for purification of DNA fragments larger than 4 kb. We have successfully used it to purify fragments around 5 kb, although the percent recovery is probably lower. For fragments larger than 5 kb, we usually use the QIAquick Gel Extraction Kit instead. One other problem that occurs when you elute the DNA in water: If you allow the column to sit for increased amounts of time during the wash step with buffer PE, you can remove too much salt from the solution and cause the DNA to be eluted as denatured single-stranded DNA fragments. Typically, I only let the wash step sit for 1-2 minutes (protocol calls for 2-5 minutes). This may not happen if you elute with buffer EB instead of water, although I have not tried this.
Qiagen also sells MinElute PCR Purification Kits and MinElute Reaction Cleanup Kits which use the same columns and are very similar to the gel extraction kit. We have used all three products and are extremely satisfied with the results. If you haven’t tried these products, you might consider purchasing a kit when your current one is finished.