purpose of this activity is to introduce the principles and
terminology of electrophoresis and demonstrate the
separation of food color dyes with agarose gel
1 plastic dish
1 slide box lid or bottom
Hot glue gun and glue
5 nine-volt batteries
1 nine-volt battery clip
2 alligator clips (1 red / 1 black)
Scissors or wire cutters
2” x 3” glass slide
Well comb (template and Styrofoam)
Tris-Borate-EDTA Buffer (TBE)
Microwave or hot water bath
Small vials or tubes
Capillary tubes with bulb
50% glycerol solution
Access the Student Journal
for Activity 7
Access the Student Presentation for Activity 7
7 - Edible Colors
Building the Electrophoresis Chamber
- Place the slide box in the center of the
plastic dish and trace around the edge with the permanent
- Extend the lines of the long sides of
the slide dish all the way up one side of the plastic dish.
Use the permanent marker to place a spot near the rim of the
plastic dish, about 1 cm out from each of the lines.
- Carefully use the large needle to punch
a hole through the plastic dish at each spot.
- Use the scissors or wire cutters to cut
two pieces of seizing wire about 10 cm longer than the length
of the plastic dish.
- Take one piece of wire and make a 90˚
bend 1 cm from the end. Be careful because the ends of the
wire will be sharp.
- Go down the wire and make another 90˚
bend so that the wire will fit down into the plastic dish and
touch both sides.
- Position the wire 1 cm above the bottom
of the plastic dish (the width of your finger) and make a 90˚
bend that will allow the wire to come out of the hole.
- Feed the end of the wire through the
hole and bend it into a loop. Cut off and dispose of any
- Repeat these steps with the second piece
of wire and the second hole.
- Place the slide box in the center of the
plastic dish to make sure that neither of the wires touches
it. Make necessary adjustment to prevent the wires from
touching the slide box. Remove the slide box.
- Plug in the hot glue gun and allow it to
heat up. Be careful when using the hot glue gun because the
gun and the glue will both get very hot.
- Use the hot glue to secure the wire at
each of the 90˚ bends. Allow the glue to dry.
- Put a thick bead of aquarium sealant
around the rim of the slide box. Place the slide box open
side down into the center of the plastic dish where you traced
it. If necessary add more sealant around the edges to make
sure there will be no leaks. The aquarium sealant will need
to dry overnight.
Building the Power Supply
- Cut the battery clip in half with the
scissors, be careful to not cut the wires.
- Using the scissors, strip away about 1.5
cm of plastic covering off the wire attached to each half of
the battery clip.
- Pull the plastic cover off one arm of
each of the alligator clips. Slide the plastic cover onto the
- Wrap the wire from the negative end of
the battery clip (red wire) around the arm of red alligator
- Slide the plastic cover back onto the
alligator clip to cover the connection.
- Repeat these steps for the black wire
and black alligator clips.
- Build a pyramid with the batteries,
three on bottom and two on top. Connect the negative ends of
the batteries to the positive ends of the opposing batteries.
- When you are ready to use the power
source attach the red wire to the empty positive end of the
battery and the black wire to the empty negative end of the
- Do not touch the alligator clips on the
end of the power supply or the buffer when the power supply is
attached to the electrophoresis chamber because it will
electrocute you. Store power supply with the batteries taken
Preparing the Gel and the Samples
- For this experiment a 1% Agarose gel was
used. Only a few milliliters of agarose gel solution are
needed per gel. Here is the recipe for 10 ml:
- Weigh 0.1 g of agarose powder on the
- Place it in the Erlenmeyer flask
- Add 10 ml of 1X TBE
- The agarose and TBE will need to be
heated in order for the agarose to dissolve. It takes about 1
minute in the microwave, or you can place the flask in a hot
water bath. When the agarose is melted, the solution will be
clear and there will be no particles floating in it.
Caution: the flask and the liquid will be very hot! Handle
- Allow the agarose solution to cool. It
will be ready when the bottom of the flask is cool enough to
touch without burning your skin.
- While the agarose solution cools, take
the glass slide and lay it on a hard, level surface.
- Take the two binder clips and the well
comb. Grip the well comb in the two binder clips so that the
comb is level and just above the glass slide.
- Take a transfer pipette and fill it with
the agarose solution. Starting at the comb and moving back,
lay the agarose solution on the slide. Be sure to: work
quickly; do not allow any gaps; do not over fill the slide
because the agarose will spill over the edge; and pop any air
- Allow the gel to cool and solidify. The
gel will turn opaque when it is set. (About 5 minutes)
- While the gel is cooling, prepare the
- Label the test tubes/vials with the
color of food dye that will be put in them. Label one for
red, blue, green, and yellow.
- In each test tube place one drop of food
dye and three drops of 50% glycerol. Repeat this for each of
- Remove the comb from the gel by gently
pulling straight up.
- When moving the gel, be very careful to
hold the slide flat. If you tilt the slide, the gel can slip
Loading and Developing the Gel
- Place the gel on top of the slide box in
the electrophoresis chamber. Make sure that the slide is
positioned so that the row of wells is parallel with the
- Pour enough TBE buffer into the
electrophoresis chamber so that it covers the gel. Do not
pour the TBE directly onto the gel; pour it to the side of the
gel in the plastic dish. If the TBE is poured directly on the
gel, it could push the gel off of the slide.
- Decide what sample you are going to put
in each well and write it down on your worksheet.
- Gently put the bulb on a capillary
tube. Be very careful when handling the capillary tubes
because they are very thin glass tubes and they break easily.
To fill the capillary tube, place the tip of it in the sample
and it will automatically draw the sample up. Be careful to
keep the sample in the capillary tube and do not let it into
the bulb. Once the tube is almost full you will need to cover
the hole on top of the bulb and squeeze the bulb just a little
to keep the sample from coming up into the bulb. Hold the
pressure steady so that you do not push the sample out of the
tube. This may take a little practice.
- Place the tip of the capillary tube into
the buffer right above the well you are going to fill. Do not
put the capillary tube into the well because, if it is bumped,
it could punch through the well leaving a hole that would leak
out the sample. Slowly squeeze the bulb more to push the
sample out of the capillary tube. The sample is heavier than
water (because you added the glycerol), so it will go straight
down into the well. Some of the sample may come out of the
well and get into the buffer. That is all right as long as
most of it is in the well. Dispose of the capillary tube in a
container designated for glass disposal.
- Repeat this step with a new capillary
tube for each of your samples.
- After all of the samples are loaded,
assemble your battery pyramid and connect the wires to the
- Clip the black alligator clip to the
loop on the wire that is behind the wells and the red
alligator clip to the loop on the wire that is in front of
wells. Do not touch the buffer while the clips are
attached! You will be electrocuted!
- Watch for bubbles to form on the wires
in the TBE. This will tell you that the current is flowing.
- Allow the gel to develop until you can
see the colors separate. The food dyes in the food colors
will travel through the gel with the electrical current
towards the red wire.
- When the gel is done developing, unclip
the alligator clips and take the battery pyramid apart.
- Remove your slide from the
electrophoresis chamber and place it onto a white paper towel
or piece of paper so you can see the colors better.
- Pour the TBE buffer into the sink.
- Observe the results of the gels.