Semi-Dry or Tank Electrotransfer

Electrotransfer refers to the standard procedure for transferring proteins from a polyacrylamide gel (SDS-PAGE) onto an Immobilon® PVDF transfer membrane. The two commonly used electrotransfer techniques are tank transfer and semi-dry transfer. Both are based on the same principles and differ only in the mechanical devices used to hold the gel/membrane stack and applications of the electrical field.

Click on the Semi-dry or Tank Electrotransfer symptoms to read about the possible causes and remedies:

Band Smeared/Distorted

Possible Cause Remedy

Membrane not uniformly wetted with methanol
  • The entire membrane must be pre-wet with methanol; the entire membrane should change uniformly from opaque to semi-transparent.

Air bubbles under membrane and between other layers in the stack

Air bubbles

Effect of air bubbles between gel and membrane during Western blot transfer step
  • Using a pipette or stirring rod, gently roll out any trapped air bubbles while assembling the stack.

Uneven contact between gel and membrane
  • Make sure entire gel and membrane surfaces are in good contact.

Too much heat generated during the transfer
  • The temperature of the run should not exceed 20 °C. For a tank transfer, pre-chill the buffer or carry out the transfer in a cold room. For a semi-dry transfer, either shorten the run time, increase the number of filter papers, or reduce the current.

Filter paper dried out during semi-dry transfer
  • Make sure filter paper is thoroughly drenched prior to transfer or use additional sheets. Be sure the stack is assembled in less than 15 minutes.

Proteins transferred too rapidly; protein buildup on the membrane surface
  • Reduce the strength of the electrical field.

High Background in Fluorescent Detection

Possible Cause                       Remedy

Autofluorescence from transfer membrane
  • Use low-autofluorescence membrane, such as Immobilon®-FL membrane, for transfer.

    Fluorescent detection of transferrin in human serum
    Reverse image demonstrating fluorescent detection of transferrin in
    human serum on various Western blot transfer

    Order Immobilon® membranes

Proteins passing through the membrane
  • Increase the time the proteins have to interact with membrane by reducing the voltage by as much as 50%.
  • Highly negatively charged proteins (due to high aspartic acid and glutamic acid content) tend to move very fast in an electric field. Decrease the voltage to slow down migration of these proteins.
  • Presence of SDS in the gel may inhibit protein binding. Equilibrate the gel in the transfer buffer for at least 15 minutes

    Equilibration improves transfer efficiency for Western blot

    Gel (top) and blot (bottom) show
    that equilibration improves transfer
    efficiency for Western blot.
  • Methanol concentration in transfer buffer is too low to facilitate removal of SDS. Increase the methanol to 15 – 20%, especially for smaller molecular weight proteins.
  • The membrane must be pre-wet with methanol; the entire membrane should change uniformly from opaque to semi- transparent.
  • Switch to Immobilon®-PSQ transfer membrane.
  • Immobilon® ordering information

Proteins retained in the gel
  • If the methanol concentration in the transfer buffer is too high, it can remove SDS from proteins and lead to protein precipitation in the gel. This would reduce the transfer of large molecular weight proteins out of the gel. If protein precipitation is an issue, the transfer buffer can be supplemented with SDS (0.01% – 0.05%) to aid in solubility. In addition, excess methanol can tend to shrink or tighten a gel, thus inhibiting transfer of large molecular weight proteins.

Isoelectric point of the protein is at or close to the pH of the transfer buffer
  • A protein that has the same isoelectric point as the pH of of the transfer buffer will have no net charge and thus will not migrate in an electric field. To facilitate transfer, try a higher pH buffer such as 10 mM CAPS buffer at pH 11, including 10% methanol or a lower pH buffer such as an acetic acid buffer.

Poor detection when urea is used in the gel and/or transfer buffer
  • Reduce the temperature by using a circulating buffer setup or run your transfer in a cold room. Urea in the presence of heat can cause carbamylation of proteins, which can change the charge of amino acids in a protein. This could affect the epitopes essential for antibody recognition and binding.

Incomplete transfer of proteins
  • Stain the gel to check for residual proteins. If transfer was not complete, review your transfer technique.

Poor protein retention
  • Once transfer is complete, be sure to dry the membrane completely to obtain optimal binding and fixation of the proteins. This should be done prior to any downstream detection method.

No Signal

Possible Cause                                           Remedy

No transfer of proteins
  • Check for the gel and membrane orientation during the transfer process.
  • Use pre-stained molecular weight standards to monitor transfer. 

Poor Transfer of Small Molecular Weight Proteins

Possible Cause                                         Remedy

Insufficient protein retention SDS interferes
with binding of small molecular weight proteins

Low methanol concentration in the transfer buffer
  • Use higher percentage of methanol (15% – 20%) in the transfer buffer.

Insufficient protein binding time
  • A lower voltage may optimize binding of small proteins to the membrane.

Current doesn’t pass through the membrane

Poor Transfer of Large Molecular Weight Proteins (~ >80 kDa)

Possible Cause                                           Remedy

Methanol concentration is too high
  • Reducing the methanol concentration to 10% (v/v) or less should help in the transfer of large molecular weight proteins by allowing the gel to swell. Moreover, a lower methanol percentage would also reduce SDS loss from the proteins and reduce protein precipitation in the gel. Proteins >200 kDa are not as sensitive to interference from the SDS in binding to membrane as are proteins <100 kDa.

Poor Transfer of Positively Charged Proteins

Possible Cause                                          Remedy

Protein net charge in the transfer buffer is
positive; proteins move toward cathode.
  • Reverse the transfer stack such that the Immobilon® transfer membrane is on the cathode side of the gel.

Poor Semi-Dry Transfer

Possible Cause  Remedy

Current bypasses the gel stack

Poor Transfer of a Wide Range of Protein Sizes

Possible Cause                                           Remedy

Different conditions required to transfer large
and small proteins
  • Refer to “Transfer of a broad MW range of proteins may require a multi-step transfer” (T. Otter et al., Anal. Biochem. 162:370-377 (1987).
  • Use three-buffer system for semi-dry transfer (View protocol on page 36 of the Protein Blotting Handbook (PDF).)