At the Institute for Basic Science (IBS) in South Korea, researchers have developed a type of MRI contrast agent that only lights up when near a target. It consists of two components, an “enhancer” which is the actual contrast agent that lights up and a “quencher” that controls the activation of the enhancer.
The enhancer remains in an “on” state as long as the quencher is at a distance, but as soon as the two are brought within 7 nanometers of each other, the contrast agent turns off and becomes invisible under MRI. Actually using these two components to visualise a target involves delivering them together, linked so that they’re near each other and so keeping the enhancer in an “off” state.
The molecular link keeping them together needs to be designed so that an enzyme that is produced by a target tumor will cut the link. Once the enhancer and quencher are disconnected, they soon move apart and find themselves at least 7 nanometers from each other, allowing the enhancer to activate and show up bright and loud on the MRI.
Of course the same method can be used to visualise not only cancer, but many other biological processes. It’s simply a matter of creating different links between the enhancer and quencher that break when in the environment of a given biological target.