Microarrays are a cutting edge technology that can rapidly identify the presence of thousands of specific DNA sequences at the same time. To make microarrays, specialised machines are used to attach bits of DNA known as probes to a small, square chip. Thousands of different probes can be added to spots on the chip, with each probe targeting a different DNA sequence. When a DNA sample is added to the chip, sequences in the sample match up to corresponding DNA fragments on the chip. When matching takes place, the paired DNA strands fluoresce, which is then read by a highly sophisticated camera. This technique can be used to rapidly identify many different GMOs at once. Although not commonly used to test for GM content today, Co-Extra researchers are looking into the possibility of using microarrays for high throughput GMO detection in the future.
Most methods used for detecting GM content look for GMO-specific DNA sequences. For some GMOs, however, it may be worthwhile to look for the genetically engineered trait in the form of proteins. Many GMOs produce proteins not found in their conventional counterparts. Bt maize, for example, could be tested with antibodies that bind to the Bt toxin itself. If the antibody binds to the target protein, the interaction could be visualised by a colour change.
Virtually all GMO testing methods detect GMOs by finding chemical differences between them and material from conventional plants. DNA targeting methods generally seek out defining genetic sequences based on the DNA strand’s chemical binding properties. For protein based testing, tests typically look at how a protein pairs up with a custom-made antibody. But there are also ways to learn more about the makeup of a sample by looking at its physical properties.
Near infrared fluorescence (NIR) detection is a method that can reveal what kinds of chemicals are present in a sample based on their physical properties. By hitting a sample with near infrared light, chemical bonds in the sample vibrate and re-release the light energy at a wavelength characteristic for a specific molecule or chemical bond. For example, if near infrared light is fired at a sample of carbon dioxide, an NIR imaging machine would pick up fluorescence (re-released light energy) with a wavelength of 0.0042 centimetres. Carbon dioxide is a simple molecule with only one kind of chemical bond. Molecules with several bonds fluoresce light at a collection of wavelengths corresponding to the chemical’s composition and complexity.
It is not yet known if the differences between GMOs and conventional plants are large enough to detect with NIR imaging. Although the technique would require advanced machinery and data processing tools, a non-chemical approach could have some advantages such as lower costs and enhanced speed and mobility.