Western blot apparatus: tanks, trays and what actually decides an even blot

Specifying the bench, from the western blot tank outwards

1. Choose wet or semi-dry from the proteins you run. A wet tank is slower, gentler and the most reliable for large proteins and for long transfers in a cold room. Semi-dry is much faster and can dry out on long runs. Laboratories running a wide size range usually keep a tank and use it for the difficult cases.
2. Treat cassettes and pads as consumables. Foam pads compress permanently and a cassette that no longer applies even pressure gives patchy transfer that looks like a gel problem. Date them when first used and replace them on that basis rather than waiting for a bad blot.
3. Buy trays sized to the membrane. Antibody incubation volume is set by the tray, and an oversized tray wastes expensive antibody on every blot. A tray that just fits the membrane, or a sealed bag, cuts antibody use substantially over a year.
4. Get the power supply right once and forget it. Constant voltage for transfer and constant current or voltage for the gel, with enough headroom for the tank's resistance. This is the item people compare and the one that least often limits a result.
5. Plan for cold and for the bench around it. Wet transfer generates heat and runs better cold, so a cold room, an ice pack insert or a cooled unit is part of the purchase. Add a rocker for incubations and a way to keep a membrane wet, because a dried membrane is a lost blot.

Whether a western blot transfer machine proves anything the tank does not

A reversible total protein stain on the membrane after transfer, photographed and kept, answers in minutes a question that otherwise takes a week of antibody troubleshooting. It also gives a better normalisation than most housekeeping proteins.

Mark the prestained ladder positions in pen immediately after transfer, because several dyes fade during blocking and the ladder is what lets a membrane be cut for two antibodies.

Buffers and the routine that keeps them honest

Prepare transfer buffer fresh, label it with the date, and do not reuse it beyond what the protocol allows. A transfer that failed because the buffer was last week's with the methanol evaporated is a recurring and preventable loss.

Methanol handling belongs in a hood and the waste has a route. For a bench running blots daily this is a real volume, and it should be planned rather than improvised.

What the western blot filter paper does in a semi dry stack

The paper is a reservoir and a pressure pad, and both jobs matter. Too thin and the stack dries part way through the transfer, which is the usual cause of a blot that is strong at the edges and faint in the middle; too thick and the field spreads and the bands blur. Thickness is a specification on the packet, so buy one grade and keep buying it.

Cut the paper to the gel rather than the cassette, soak it until no bubbles rise from it, and roll the stack rather than pressing it flat. A single bubble between paper and membrane leaves a clear circle that no antibody optimisation will fill in.

Choosing western blot gels for the apparatus you own

Precast gels and hand cast gels both work, and the choice is about reproducibility against cost and flexibility. A precast gel removes the two variables that move most between people, acrylamide concentration and polymerisation time, which is worth paying for where several people run the same assay. Hand cast gels earn their place when the resolution needed is at the ends of the range, because a gradient or an unusual percentage is not something a catalogue stocks.

What is not negotiable is that the gel format fits the cassette and the comb fits the loading volume. A gel a millimetre too thick transfers unevenly, and that shows up as the same lanes being weak on every blot.

When a western blot membrane PVDF choice beats nitrocellulose

The fluoride membrane binds more protein per unit area, tolerates stripping and reprobing, and survives being dried and stored, which is why it is the default where a blot will be asked a second question. It needs wetting in alcohol before it will take buffer, and a membrane that was allowed to dry in the middle of a transfer keeps a permanent mark where it did.

Nitrocellulose gives a lower background with some antibodies and is the easier membrane for a low abundance target read by fluorescence. Neither is better in general; what matters is that one is chosen per assay and then not changed halfway through a series.

Common questions

Wet tank or semi-dry transfer?

A wet western blot tank for large proteins, long transfers and the most reliable result; semi-dry for speed on routine sizes. Many laboratories own both and use the tank for the difficult cases.

Why are my transfers patchy?

Usually the pads or the cassette rather than the settings. Compressed pads apply uneven pressure, and paper cut larger than the gel lets current bypass the sandwich. Both are cheap and both are ignored for years.

Does the western blot tray matter?

For antibody cost, considerably. Incubation volume is set by the tray, so one sized to the membrane, or a sealed bag, cuts primary antibody use on every blot with no downside.

What else limits a blotting bench?

A rocker, enough trays to run several blots at once, a way to keep membranes wet, and cold transfer capacity. None is expensive and each of them is what actually slows a busy bench down.

Does a western blot rocker matter?

For the incubations, yes, more than people expect. An antibody solution that is not moving depletes locally, and the result is a blot that is stronger where the liquid happened to circulate. A slow orbital or rocking platform that keeps the whole membrane covered is enough; speed is not the point, coverage is.

Is a nitrocellulose membrane western blot better for small proteins?

Often, because the smaller pore size holds a low molecular weight target that can pass through a larger pore membrane during a long transfer. The other half of the answer is the transfer time: a small protein is lost by transferring for as long as a large one needs, whichever membrane is used.

Browse by service class

• Compare Gene synthesis on advertised prices