The Bio-Rad Trans-Blot Semi-Dry System provides an efficient way to transfer proteins to nitrocellulose membranes with less preparation time, material use or clean-up as compared to wet transfer cell counterparts. The minimal amount of buffer required for the transfer (about 250 ml per experiment), saves money and reagents. Moreover, unlike longer wet transfers, this semi-dry system does not require the user to pre-chill a large quantity of transfer buffer, since all buffers used with this system can be stored at room temperature. Also, the Bio-Rad Trans-Blot Semi-Dry System affords a large surface area (20 x 18.5 cm) for blotting and allows the user to transfer up to 3 small gels and 2 large gels at a time.
What makes this system so convenient is really the speed of transfer. I have found that I can efficiently transfer mini-gels, either pre-cast or self-prepared, in 15 min at 15 V and large gels in 30 min at 25 V. The transfer is easy to set up with minimal equilibration time required for the gel, blotting paper and nitrocellulose membrane. Bio-Rad recommends that you equilibrate for at least 5 min, but I have found that 1 min is sufficient in most cases. If you find that your marker and protein are not transferring to their full potential, decreasing the amount of methanol in the buffer may help.
The main downfall that I have found with repeated use of this system is that some low molecular weight molecules will transfer through the membrane without quantitative binding and larger molecules (greater than 110 kD) may sometimes not transfer well. I have improved the efficiency of larger molecule transfer by running less protein on the gel and separating it much farther than usual. Also, I have been disappointed to determine that the transfer efficiency onto PVDF is poor and, despite testing many different buffer variations, I have not been able to troubleshoot this problem very well. Therefore, if you need to strip and re-probe a membrane many times, I recommend transferring onto PVDF using the Bio-Rad Mini Trans-Blot Electrophoretic Transfer System.
The Trans-Blot Semi-Dry system is still a must purchase for every lab that does blotting and can now also be used to transfer DNA and RNA making it a great purchase for use in multiple procedures. In order to transfer both DNA and RNA from agarose gels, you will have to purchase an additional support frame that protects agarose gels from both compression and breakage due to the tight squeezing electrodes used in the apparatus. When using the system to transfer from agarose gels, I have found best transfer in Northern and Southern blotting in 30 min. This is much faster and easier to set up compared to older protocols. Therefore, although you will need to make the additional part purchase, I feel that this is a must needed commodity for labs performing northern or southern blotting.
Amy Bellmeyer, M.S.
Research Technician
Division of Pulmonary and Critical Care Medicine
Northwestern University