QuantaLife, which was recently acquired by Bio-Rad Laboratories, produces an innovative droplet digital PCR system that provides quantification of target molecules with unprecedented precision and sensitivity. In the videos that follow, QuantaLife’s VP of Application Development Dr. Serge Saxonov, introduces Droplet Digital™ PCR and explains various aspects of the technology.
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Protein blotting is a staple technique of most molecular biology and proteomics laboratories. In previous posts, we discussed topics such as semi-dry protein transfer and protein transfer methods, and we even did a multi-part series on western blotting.
Now, we are proud to present you with a 43 page protein blotting guide put together by Bio-Rad Laboratories. The guide is organized into two parts which cover the theory and methods behind protein blotting. You will learn topics such as methods and instrumentation, the difference between various membranes and tranfer buffers, the ins and outs of transfer conditions, detection and imaging and a host of different blotting and detection protocols.
The guide is fairly technical and is appropriate for both novice and advanced users alike.
Click on the link to download the Protein Blotting Guide now.
With its proprietary transfer buffer, the Trans-Blot Turbo system generates very fast transfer even for high molecular weight proteins. However, as indicated previously, the gel composition, i.e. the acrylamide – bis-acrylamide network density, influences the transfer efficiency. A protein can more easily move out of the gel during the transfer if it is located in a portion of gel that has the widest pore structure. As proteins above 150 kD are always located on the first top part of a gel, the most efficient transfer of those large proteins is achieved when using gradient gel with a concentration of 4% of acrylamide – bis-acrylamide at the top of the gel. The transfer efficiency of proteins from an Any kD homogeneous acrylamide gel and a 4-20% gradient gel is illustrated.
In theory, increasing the power input and duration of an electrophoretic transfer results in the transfer of more protein out of a gel.
In practice, however, test runs should be used to evaluate transfer efficiency at various field strengths and transfer times for each set of proteins of interest.
The optimum transfer conditions depend on a number of factors, including the size, charge and electrophoretic mobility of the protein, the type of gel and transfer buffer used, and the type of transfer system being used.
In a semi-dry transfer system, the distance between electrodes is determined only by the thickness of the gel-membrane sandwich, and buffering and cooling capacity is limited to the buffer in the filter paper. As a result, the field strength is maximized in semi-dry systems, and the limited buffering and cooling capacity restricts the transfer time. Though power conditions may be varied with the power supply, semi-dry transfers often operate best within a narrow range of settings.
In semi-dry systems, the distance between the electrodes is limited only by the thickness of the gel and membrane sandwich. As a result, high electric field strengths and high-intensity blotting conditions are achieved. Under semi-dry conditions, some small proteins may be driven throughout the membrane in response to the high field strengths. Moreover, because low buffer capacity limits run times, some large proteins may be poorly transferred. Use of a discontinuous buffer system may enhance semi-dry transfer of high molecular weight proteins (>80 kD). As semi-dry transfers require considerably less buffer and are easier to set up than the tank method, laboratories performing large numbers of blots often favour them.
Novel buffer and material formulations have been developed that can be used with higher electric field strengths than those used in typical semi-dry blotting. These conditions yield complete and extremely rapid transfer, with some systems completing transfer in 3 – 10 min. Such rapid blotting systems do not incorporate external cooling mechanisms, so the high power dissipation may generate more heat than other techniques. Rapid blotting systems are intended for extremely rapid transfers where heat-induced protein denaturation will not affect downstream applications.
The Trans-Blot Turbo system performs semi-dry transfers in as little as 3 min. The system uses prepackaged transfer packs containing a prewet membrane (nitrocellulose or polyvinylidene difluoride:PVDF) and filter paper stacks soaked with a proprietary buffer that allows this fast and efficient transfer. The base unit contains an integrated power supply that drives two independent transfer cassettes, allowing transfer of a total of four mini-format or two midi-format gels. As the transfer cassette electrodes are made with robust permanent stainless-steel and platinum-coated titanium, the Trans-Blot Turbo system also has the flexibility to run traditional semi-dry protocols with hand-made buffers and any membrane, as any semi-dry system.
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