Most detection mechanisms involved in small molecule sensors comprise some modulation in the fluorescent behavior of the sensing molecule upon binding the target metal. When a metal coordinates to such a sensor, it may either enhance or reduce the original fluorescent emission. The former is known as the Chelation Enhancement Fluorescence effect (CHEF), while the latter is called the Chelation Enhancement Quenching effect (CHEQ). By changing the intensity of emission at different wavelengths, the resulting fluorescent spectrum may attenuate, amplify, or shift upon the binding and dissociation of a metal. This shift in spectra can be monitored using a detector such as a microscope or a photodiode.
Listed below are some examples of mechanisms by which emission is modulated. Their participation in CHEQ or CHEF is dependent on the metal and small molecule sensor in question.