Figure 1.

A receptor–fluorophore molecule can exhibit low fluorescence because of FRET-induced quenching (left half), which is an interaction between an energy acceptor, also known as a quencher, and a fluorophore. When a glucose molecule reversibly binds to the receptor part of the molecule (right half), then the FRET becomes disrupted because of decreased electron sharing between the two interacting groups. In the absence of FRET, quenching of the fluorophore ceases and the fluorophore becomes highly fluorescent.