Lateral Flow Strip Test
The remainder of this lesson will focus the on lateral flow strip method, applying all of the principles we have discussed up to this point. Let’s describe the lateral flow test for the Bt protein. You will also want to refer to the lateral flow strip animation.
First a gold particle is linked to the antibody specific for the Bt protein. This antibody can perform as it does in the immune system by binding to the Bt protein if the protein is present in a test tube (detector antibody). How do we get the Bt protein in a test tube? We simply take a bit of tissue smaller than a dime from the plant and chop it up in a plastic tube in a water solution, or alternatively as shown in Figs. 12-13, seeds can be ground up. The proteins in the sample will come out of the cells and dissolve or suspend in the solution. Some food products may also be ground and used for a protein detection test. This resulting solution in our example of plant cell proteins is mixed with the antibody and if the Bt protein is present, the antibody will bind to it (Fig. 14).
Figure 12 Testing for the presence of a GMO protein in soybean seeds.
Figure 13 Grinding up the seed sample, placing one GMO seed into a sample with 800 non-GMO seeds.
Figure 14 Placing a lateral flow strip into the seed solution.
The solution containing the plant proteins is transferred to a filter stick that has a second Bt antibody imbedded in it (capture antibody). These antibodies will bind to a different part of the Bt protein and do not have the gold label. As the solution is wicked up the strip, Bt proteins encounter the capture Bt antibody and are adsorbed. All other proteins are washed away (Fig 14).
The final step is to assay for the presence of the Bt protein. The gold linked to the first antibody (which is still stuck to the Bt protein) will become concentrate and a pink color appears on the filter stick. Gold is a pinkish color in its natural state. If no Bt protein is present, no color appears. The diagram in Figure 15 will help you understand how these work.
Figure 15 Formation of color in the Bt lateral flow strip.
The filter stick described in the animation actually consists of two stacked filters. We just described what happens in the bottom filter. A positive control filter is also used to make sure everything has been added and the color reagents are working. This filter gives a dark color in all tests done correctly. If this filter stays white, something is wrong with the procedure or the test strip (Fig 16). By developing a test kit such as this, the scientist has provided the farmer or agronomist with a useful tool to determine if a corn plant is making the Bt protein.
Figure 16 Visualizing the final result.
The lateral flow strip test procedure can be applied to any genetically engineered plant that is making a protein that is in some way different than the proteins it “naturally” makes. Not all kits will work exactly as described above, but the basic idea is the same. The protein can be detected if it is made in the tissue sampled. The decision to develop detection kits will depend upon the needs perceived by the company developing the transgenic crops or perhaps the eventual users of the crop.
*This animation has no audio.*