How to Make an Electrophoresis Gel

Electrophoresis is the term used for the study of the way charged particles move through a medium when subjected to an electrical field. The particles will travel through the gel at different speeds, depending on the charge carried by the particle and the size of the particle that must push through the somewhat restrictive medium. The medium is intentionally made restrictive so that the particles will form a pattern in the medium that can be analyzed when the electric field is removed. This technique is valuable in medical research to separate RNA, DNA and proteins based on their capabilities to move through the gel. Use these tips to learn how to make an electrophoresis gel.


  1. 1
    Find the gel concentration required. This must be specified by the physician and will vary based on the type of testing required by the study the physician is performing. Common concentrations are 0.7 percent. 0.8 percent, 1.0 percent and 1.2 percent.
  2. 2
    Obtain an electrophoresis gel casting tray. These trays are available at medical supply outlets. Note the volume of the tray because it will determine the maximum amount of electrophoresis gel that can be made at once.
  3. 3
    Gather the required chemicals. Get an amount of Tris-Acetate-EDTA (TAE) sufficient to make up the volume of the gel being made. The amount of agarose, the polymer that forms the gel, will depend on the concentration of the gel to be made. The expressed gel percentage is agarose in grams divided by TAE in mL. The final ingredient needed is ethidium bromide (EtBr). EtBr makes DNA visible under ultraviolet light. Divide the amount of TAE used by 1000 to determine the amount of EtBr needed.
  4. 4
    Add the agarose. Add the determined amount of agarose to the required amount of TAE. Gently stir or swirl the mixture to ensure proper mixing.
  5. 5
    Prepare the mixture. The agarose in TAE must be heated in a microwave oven to dissolve it. Warm the solution for short periods of time, such as 15 seconds, on low power. Check the progress of the melting constantly. If the TAE is warmed to the point where particulate matter is formed, the batch has been ruined.
  6. 6
    Add the EtBr. EtBr is a powerful biohazard. Laboratory gloves should be worn for this part of the process. Add the EtBr after heating of the TAE has been completed. Gently stir or swirl the container to ensure proper mixing. Allow the liquid to stand and cool for 5 minutes.
  7. 7
    Fill the casting trays. Swirl or stir the chemical mixture to ensure that there is uniform temperature throughout the mixture. Pour the mixture carefully in to the casting tray.
  8. 8
    Insert the combs. Place the casting combs into the support rails of the casting tray. The comb teeth will create wells in the gel to which the sample to be tested can be added. The combs come in various sizes to create various size wells. The size wells that need to be formed will be determined by the physician based on the study to be performed.
  9. 9
    Allow the casting trays to cool and the gel to set for 1 hour. Remove the casting combs. Remove the gel from the casting tray. The electrophoresis gel is now ready for use.


  • Ethidium bromide (EtBr) is a potent mutagen. Avoid getting it anywhere on the skin. Avoid spilling it around the work area.
  • The TAE will be hot coming from the microwave. The liquid TAE container should be handled carefully.

Things You'll Need

  • Tris-Acetate-EDTA (TAE)
  • Agarose
  • Ethidium Bromide (EtBr)
  • Electrophoresis gel casting tray
  • Laboratory safety gloves
  • Microwave oven

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Categories: Science